Scintillating hybrid material, associated part, associated device and associated apparatus, methods for producing or measuring same

ABSTRACT

Hybrid material for plastic scintillation measurement comprising:
         a polymeric matrix; and   a fluorescent mixture incorporated in the polymeric matrix and comprising, with respect to the total number of moles of primary fluorophore in the incorporated fluorescent mixture, i) from 95.6 molar % to 99.6 molar % of a main primary fluorophore consisting of naphthalene and ii) from 0.4 molar % to 20 molar % of an additional primary fluorophore.       

     The decay constant of the fluorescence of the hybrid material is intermediate between that of a fast plastic scintillator material and of a slow plastic scintillator material. Further, they can be chosen over a wide range. 
     The invention also relates to an associated part, device and item of equipment, to their processes of manufacture or their methods of measurement.

TECHNICAL FIELD

The present invention belongs to the field of the measurement ofradioactivity by the plastic scintillation technique.

The invention more particularly relates to a material for themeasurement by plastic scintillation, to a part comprising the materialand to its associated measurement device or item of equipment, to apolymerization composition, to the kits for the manufacture of thematerial, to the associated manufacturing processes and also to themethod for measurement by plastic scintillation using the device.

Technical Background

The plastic scintillation measurement consists in determining thepresence and/or the amount of one or more radioactive substances, amongothers in physics, geology, biology or medicine, for dating,environmental monitoring or control of the nonproliferation of nucleararms.

In practice, the radioactive substance emitting an ionizing radiation oran ionizing particle (alpha particle, electron, positron, photon,neutron, and the like) is exposed to a scintillating material known as“plastic scintillator” which converts the energy deposit resulting fromthe radiation/substance interaction into light radiation (known as“radioluminescent” radiation) which can be measured by a photon-electronconverter having gain, such as, for example, a photomultiplier.

The plastic scintillator has been known since the middle of the XXthcentury. It is described, for example, in the document “Moser, S. W.;Harder, W. F.; Hurlbut, C. R.; Kusner, M. R.; “Principles and practiceof plastic scintillator design”, Radiat. Phys. Chem., 1993, vol. 41, No.1/2, 31-36” [reference 1] and “Bertrand, G. H. V.; Hamel, M.; Sguerra,F.; “Current status on plastic scintillators modifications”, Chem. Eur.J., 2014, 20, 15660-15685” [reference 2]. It is generally provided inthe form of a polymeric matrix into which a primary fluorophore, indeedeven a secondary fluorophore, is inserted. A fluorophore is a chemicalcompound capable of emitting visible fluorescence light after excitationby photons or other incident particles. The primary fluorophore and thesecondary fluorophore are constituted by an aromatic molecule withfluorescent properties (molecule known as fluorophore) making possiblescintillation detection.

The main role of the polymeric matrix is to be a support capable ofreceiving the energy of the ionizing radiation or of the ionizingparticle. After recombination of the excited and/or ionized entitieswhich are then formed, this energy is converted into radioluminescentradiation and then transferred to the primary fluorophore and optionallyto the secondary fluorophore, which can increase the wavelength of theradiation emitted by the primary fluorophore in order to improve thedetection thereof.

A specific plastic scintillator of phoswich type (anglo-saxon neologismresulting from the combination of the terms phosphorus and sandwich,generally translated to mean “sandwich scintillator”) was proposed fromthe beginning of the development of plastic scintillators in thedocument “Wilkinson D. H., “The Phoswich—A Multiple Phosphor”, Rev. Sci.Instrum. 1952, 23, 414-417.” [reference 3].

For the purpose of obtaining novel scintillation properties, a phoswichscintillator combines at least two compartments: on the one hand, acompartment comprising a slow scintillator (high fluorescence decayconstant, generally comprised between 200 ns and 1000 ns) and, on theother hand, another compartment comprising a fast scintillator (muchlower fluorescence decay constant, generally of between 2 ns and 7 ns).

Nevertheless, such a scintillator poses at least one of the followingproblems:

-   -   the difference between the fluorescence decay constant of the        fast compartment and that of the slow compartment is too low:        the separation of the scintillation pulses between these stages        is then not possible electronically;    -   the difference between the fluorescence decay constant of the        fast compartment and that of the slow compartment is too great:        the scintillation pulse of the slow scintillator can be        partially or completely masked in the electronic background        noise of the scintillating pulse acquisition device, which can        result in erroneous values being obtained;    -   the luminescent signal is acquired over a period of time which        is typically of approximately 6 to 10 times the fluorescence        decay constant of the slow compartment. In the event of a high        count rate due to the multiplicity of the ionizing particles or        the high intensity of the ionizing radiation in interaction with        the phoswich scintillator, the probability of pile-up (that is        to say two pulses present in the same acquisition time window)        of the scintillation pulses becomes increasingly high. For this        reason, it might be that several pulses appear in the same        acquisition time window, which results in rejection of the        pile-ups by a phenomenon of saturation of the acquisition        electronics, and thus in an underestimation of the count rate.

DESCRIPTION OF THE INVENTION

One of the aims of the invention is thus to avoid or alleviate one ormore of the disadvantages described above by providing a novel type ofconstituent material of a plastic scintillator referred to as “hybridmaterial”.

The present invention relates to a hybrid material for plasticscintillation measurement comprising (indeed even consisting of):

-   -   a polymeric matrix; and    -   a fluorescent mixture incorporated in the polymeric matrix and        comprising, in a molar concentration with respect to the total        number of moles of primary fluorophore in the incorporated        fluorescent mixture:

i) from 80 molar % (more specifically 80.0 molar %) to 99.6 molar % of amain primary fluorophore consisting of naphthalene; and

ii) from 0.4 molar % to 20 molar % (more specifically 20.0 molar %) ofan additional primary fluorophore, the centroid of the light absorptionspectrum and of the fluorescence emission spectrum of which respectivelyhave a wavelength comprised between 250 nm and 340 nm and comprisedbetween 330 nm and 380 nm, the fluorescence decay constant of which iscomprised between 1 ns and 10 ns, and the fluorescence quantum yield ina nonpolar solvent of which is greater than 0.2, typically comprisedbetween 0.2 and 1; preferentially greater than 0.5, typically comprisedbetween 0.5 and 1.

The hybrid material of the invention can also exclude certain compounds,among others when this material is employed according to the inventiondescribed below, among others for the part, the device, the item ofequipment and their associated processes. More particularly, it does notcomprise one or more of the following compounds, in particular withrespect to the total weight of material:

-   -   a polymerization initiator, such as, for example, a        photoinitiator, particularly TPO        (2,4,6-trimethyl-benzoyl(diphenyl)phosphine oxide), more        particularly 0.5% by weight of TPO. This is because the use of a        photoinitiator to initiate the polymerization can result in        scintillators with a lower scintillation yield, indeed even        containing fluorophores subject to photobleaching by the photon        activation source; and/or    -   15% of naphthalene, 1.5% of PPO, 0.08% of POPOP, 0.5% of TPO and        the remainder of TMPTA (ethoxylated trimethylolpropane        triacrylate); and/or    -   10% of naphthalene, 0.1% of PPO, 0.1% of POPOP and the remainder        of polystyrene; and/or    -   a metal compound (namely an inorganic or organometallic        compound) comprising a metal element chosen, for example, from        lead, tin, bismuth or their mixtures. Such a metal element can        reduce the scintillation yield; and/or    -   a secondary fluorophore.

One or more of the exclusions of these compounds may also apply to thepolymerization composition and/or to the ready-for-use kit according tothe invention as are described below.

A nonpolar solvent suitable for a fluorescence quantum yield measurementis, for example, cyclohexane, toluene, dichloromethane, xylene or anyxylene isomer.

The material for the plastic scintillation measurement according to theinvention can also be denoted in the present description by theexpression “plastic scintillator”. It is known as “hybrid” because itsfluorescence decay constant is intermediate between that of a fastplastic scintillator and of a slow plastic scintillator. Advantageously,the value of this constant can further be chosen optimally during themanufacture of the hybrid material in an intermediate range comprisedbetween 10 ns and 90 ns (preferentially between 15 ns and 80 ns), forvalues between these two extremes which, to the knowledge of theinventor, are not obtained with the classic scintillators currentlymarketed. It can particularly be chosen between 25 ns and 75 ns, moreparticularly between 28 ns and 70 ns.

This tunability in time of the fluorescence decay constant of the hybridmaterial is rendered possible by virtue of the use of a specificfluorescent mixture. This mixture is characterized among others by thecombined choice of naphthalene as main primary fluorophore and of anadditional primary fluorophore having specific photophysical properties,and also by the choice of a defined concentration ratio between thesetwo primary fluorophores.

Unexpectedly, as shown by the implementational examples, the mainprimary fluorophore and the additional primary fluorophore actsynergistically to very substantially vary, while using a reducedconcentration range for the additional primary fluorophore, thefluorescence decay constant. Further, the relative simplicity of thissystem, which requires essentially this combination between these twoprimary fluorophores, avoids the addition of an additional possiblydisruptive or expensive molecule. These advantageous properties make thehybrid material of the invention a particularly effective material forthe plastic scintillation measurement which can be easily produced on anindustrial scale at a moderate cost.

Contrary to the improvement routes followed by the state of the art, theinvention does not consist of the use of a novel polymeric matrix, theaddition of additive to the plastic scintillator or the development asprimary fluorophore of novel families of molecules (“quantum dots”,organometallic complexes, nanoparticles, and the like) in order toovercome at least one of the abovementioned disadvantages but identifiesthe fluorescent mixture of the invention which makes possible access toa hybrid material. All of the characteristics necessary to the materialfor the plastic scintillation measurement according to the invention canthus be essentially limited to a polymeric matrix and to theincorporated fluorescent mixture. The composition of the plasticscintillator is thus simplified by being freed from the difficulty invery precisely determining the appropriate proportion between a primaryfluorophore and a secondary fluorophore for the purpose of obtainingradioluminescence radiation and a fluorescence decay constant which areoptimized. Thus, as indicated above, according to a specific embodiment,the hybrid material of the invention does not comprise a secondaryfluorophore.

At the molecular scale, the plastic scintillator of the invention can beregarded as a pseudoliquid as the chains of the polymers constitutingall or part of the polymeric matrix are labile and allow a degree offreedom of movement to the different constituents of the plasticscintillator. At the macroscopic scale, the plastic scintillatornevertheless retains sufficient mechanical strength for the purpose ofmanufacturing a part for scintillation detection.

The invention is completed by the following subject matters and/orcharacteristics, taken alone or according to any one of theirtechnically possible combinations.

In the present description of the invention, a verb such as “tocomprise”, “to incorporate”, “to include”, “to contain” and itsconjugated forms are open terms and thus do not exclude the presence ofadditional element(s) and/or step(s) which are added to the initialelement(s) and/or step(s) stated after these terms. However, these openterms are further targeted at a specific embodiment in which only theinitial element(s) and/or step(s), with the exclusion of any other, aretargeted; in which case the open term further targets the closed term“to consist of”, “to constitute”, “to compose of” and its conjugatedforms.

The use of the indefinite article “a” or “an” for an element or a stepdoes not exclude, unless otherwise mentioned, the presence of aplurality of elements or steps, in such a way that the expression “oneor more” can be substituted for it.

Any reference sign in brackets in the claims should not be interpretedas limiting the scope of the invention.

The expression “according to one or more of the alternative formsdescribed in the present description” for a material/an element refersamong others to the alternative forms which relate to the chemicalcomposition and/or to the proportion of the constituents of thismaterial and that any additional chemical entity which it may possiblycontain and among others to the alternative forms which relate to thechemical composition, the structure, the geometry, the arrangement inspace and/or the chemical composition of this element or of aconstituent subelement of the element. These alternative forms are, forexample, those indicated in the claims.

Furthermore, unless otherwise indicated:

-   -   the values at the limits are included in the ranges of        parameters indicated;    -   except when a margin of error is indicated, the margins of        uncertainty for the values mentioned are such that the maximum        error for the final figure indicated has to be estimated from        the convention relating to rounding up. For example, for a        measurement of 3.5, the margin of error is 3.45-3.54;    -   the temperatures indicated are considered for an implementation        at atmospheric pressure;    -   any percentage by weight of a component of the plastic        scintillator refers to the total weight of the plastic        scintillator, the remainder being constituted by the polymeric        matrix.

The polymeric matrix of the hybrid material of the invention iscompletely or partially composed of at least one polymer comprisingrepeat units resulting from the polymerization of monomers or oligomers(which can themselves originate from the polymerization of monomers).The chemical structure of the repeat units is thus similar to thechemical structure of the monomers, the latter structure having onlybeen modified by the polymerization reaction. In the presentdescription, a polymer is a general term which can respectively denote ahomopolymer or a copolymer, namely a polymer which can comprise repeatunits of identical or different chemical structure.

The monomer or oligomer comprises, for example, at least one aromatic(among others, for making use of its photophysical properties),(meth)acrylic (namely acrylic or methacrylic) or vinyl group. Apolymerizable group can be a group comprising an unsaturated ethylenecarbon-carbon double bond, such as, for example, the (meth)acrylic orvinyl group. Further, this polymerizable group must be able to bepolymerized according to a radical polymerization.

More specifically, at least one monomer can be chosen from styrene,vinyltoluene, vinylxylene, 1-vinylbiphenyl, 2-vinylbiphenyl,1-vinylnaphthalene, 2-vinylnaphthalene, 1-methylnaphthalene,N-vinylcarbazole, methyl (meth)acrylate, (meth)acrylic acid or2-hydroxyethyl (meth)acrylate, indeed even more generally an alkylmethacrylate, the linear or branched alkyl group of which comprisesbetween 1 and 20 carbon atoms.

Preferably, the monomer is styrene or vinyltoluene in order to form thecorresponding homopolymer.

Advantageously, the monomer can be chosen more particularly from amolecule having properties of specific fluorescence, for example1-vinylbiphenyl, 2-vinylbiphenyl, 1-vinylnaphthalene,2-vinylnaphthalene, 1-methylnaphthalene, N-vinylcarbazole or theirmixtures.

According to a specific embodiment, the polymeric matrix of the hybridmaterial of the invention does not completely or partially comprise atleast one polymer comprising repeat units resulting from thepolymerization of monomers or oligomers comprising a triacrylate and/ortrimethacrylate group; which excludes from the polymeric matrix apolymer such as, for example, TMPTA (ethoxylated trimethylolpropanetriacrylate), in particular ethoxylated (15) TMPTA. Advantageously, thismakes it possible to exclude a polymer having brittle mechanicalproperties.

The polymeric matrix can be constituted, completely or partially(preferably more than 10% by weight of polymer in the polymeric matrix),of at least one crosslinked polymer (for example by means of acrosslinking agent) in which polymeric chains are connected together bycrosslinking bridges, in order, among others, to improve the mechanicaland/or scintillation properties. The crosslinking agent can be a monomercomprising at least two polymerizable functionals capable, afterpolymerization, of forming a bridge between two polymer chains. It canbe chosen from divinylbenzene, an alkyl diacrylate or an alkyldimethacrylate, the hydrocarbon chain of these last two containingbetween 2 and 20 carbon atoms.

Preferably, the crosslinking agent is 1,4-butanediyl dimethacrylate ordivinylbenzene.

After polymerization of the crosslinked polymer, apart from theabovementioned repeat units, the copolymer obtained can comprise repeatunits resulting from the polymerization of the crosslinking agent.

As regards one of the other main constituents of the hybrid material ofthe invention, which is the fluorescent mixture incorporated in thepolymeric matrix, the hybrid material can comprise from 1% by weight to25% by weight of the incorporated fluorescent mixture, indeed even from1% by weight to 5% by weight of the incorporated fluorescent mixture,with respect to the total weight of hybrid material. Above aconcentration by weight of 25%, an exudation, namely a sweating of thefluorescent mixture out of the plastic scintillator, may take place.

The concentration by weight of the fluorescent mixture incorporated inthe hybrid material can be easily calculated by determining the weightof the polymeric matrix.

One of the methods of a person skilled in the art is as follows: themolar concentration of the monomers and of the oligomers in thepolymerization medium is known in advance or can be determined by aquantitative measurement method, such as UV spectrophotometry. Thecorresponding concentration by weight is subsequently calculated fromthe molecular weights. In point of fact, the monomers, the oligomers ortheir mixtures form the polymeric matrix according to a polymerizationyield which can be measured beforehand but which is generally greaterthan 95%, indeed even 98%, indeed even generally equal to 100%.Consequently, the proportion by weight of the monomers and of theoligomers present in the polymeric matrix is equivalent to this reactionyield, multiplied by the concentration by weight determined beforehand.A person skilled in the art can thus easily, using his generalknowledge, convert a concentration by weight into a molar concentrationfor all of the constituents of the hybrid material.

The percentages by weight or the molar percentages of the incorporatedfluorescent mixture, of the main primary fluorophore, of the additionalprimary fluorophore, of the secondary fluorophore or of an additionalcompound can be determined a posteriori in the hybrid material by ananalytical technique, such as, for example, solid-state Nuclear MagneticResonance (NMR). Another technique consists in dissolving the plasticscintillator in dichloromethane, precipitating, from methanol, theconstituent polymer of the polymeric matrix, filtering the mixtureobtained, in order to recover the molecule, the concentration of whichit is desired to measure, then quantifying it by elemental analysis withdetection of a specific constituent atom of this molecule.

The incorporate of the fluorescent mixture in the polymeric matrix canbe carried out according to several embodiments. In particular, at leastone fluorescent molecular chosen from the main primary fluorophore, theadditional primary fluorophore or their mixtures can be incorporated inthe polymeric matrix by dispersion or by grafting of this molecule inthe polymeric matrix. In the case of the grafting, the fluorescentmolecule (generally the additional primary fluorophore) is covalentlybonded to the polymeric matrix. This covalent bond is formed, forexample, during the manufacture by polymerization of the polymericmatrix, the fluorescent molecule comprising at least one polymerizablefunctional.

Optionally, the hybrid material of the invention can contain one or moresubstances not having a significant impact on the plastic scintillationmeasurement with the hybrid material of the invention or improving someof its properties. Just like the incorporated fluorescent mixture, thesesubstances are generally homogeneously or nonhomogeneously dispersed inthe hybrid material.

The decay constant of the hybrid material of the invention is conferredby that of the incorporated fluorescent mixture. Thus, the incorporatedfluorescent mixture, and thus the hybrid material, can have afluorescence decay constant comprised between 10 ns and 90 ns, indeedeven comprised between 15 ns and 80 ns, advantageously comprised between30 ns and 80 ns, particularly between 25 ns and 75 ns, more particularlybetween 28 ns and 70 ns.

Preferentially, the incorporated fluorescent mixture comprises from 90molar % to 99.1 molar % of the main primary fluorophore (morespecifically, from 90.0 molar % to 99.1 molar % of the main primaryfluorophore and thus from 0.9 molar % to 10.0 molar % of the additionalprimary fluorophore), more preferentially still from 96 molar % to 99.1molar % of the main primary fluorophore (more specifically from 96.0molar % to 99.1 molar % of the main primary fluorophore and thus from0.9 molar % to 4.0 molar % of the additional primary fluorophore): thisjudiciously chosen concentration of main primary fluorophore and thecomplementary concentration of additional primary fluorophore confer, onthe incorporated fluorescent mixture and thus on the hybrid material, afluorescence decay constant which can respectively be, at theseconcentration ranges, comprised between 16 ns and 74 ns, morepreferentially still between 30 ns and 70 ns.

Preferably, the incorporated fluorescent mixture comprises i) from 95.6molar % to 99.1 molar % of the main primary fluorophore consisting ofnaphthalene and ii) from 0.9 molar % to 4.4 molar % of the additionalprimary fluorophore. According to this concentration range, thefluorescence decay constant of the hybrid material of the invention canbe comprised between 25 ns and 75 ns, more particularly between 28 nsand 70 ns.

These preferential concentration ranges of primary fluorophores can thusconfer, on the hybrid material, an increasingly high fluorescence decayconstant: such a hybrid material can then advantageously participate inthe composition of a hybrid plastic scintillator compartment, optionallycombined with a fast plastic scintillator compartment, in a device fordetection by plastic scintillation of phoswich type, for improving thediscrimination between beta particle and gamma radiation. Theyfurthermore represent a good compromise between the scintillation yieldand the tunability of the hybrid material of the invention.

For example, the variable molar concentrations of the main primaryfluorophore in the incorporated fluorescent mixture (the remainder ofthe mixture being constituted by the additional primary fluorophore) canoptionally confer, on the hybrid material, the following fluorescencedecay constants:

-   -   molar concentration of 86%: 15 ns;    -   molar concentration of 95.6%: 28 ns;    -   molar concentration of 96%: 35 ns;    -   molar concentration of 99%: 80 ns;    -   molar concentration of 100%: 90 ns.

Preferentially, the additional primary fluorophore has a fluorescencedecay constant (generally denoted “tau”) comprised between 1 ns and 10ns, has a light absorption spectrum and a fluorescence emissionspectrum, the centroid of which is respectively at a wavelengthcomprised between 250 nm and 340 nm and comprised between 330 nm and 380nm, and the fluorescence quantum yield of which in a nonpolar solvent iscomprised between 0.5 and 1.

In the present description, the centroid denotes the wavelength for themiddle of the full width at half maximum of the band of greateramplitude of the radiation under consideration. A light absorptionspectrum can be measured with a UV/visible spectrophotometer and afluorescence emission spectrum can be measured with aspectrofluorometer.

The fluorescence decay constant corresponds to the variation over timeof the photoluminescence intensity. It is measured by time-correlatedsingle photon counting; as described, for example, in the document “M.Wahl, “Time-Correlated Single Photon Counting”, M. Wahl, Technicalinstructions from PicoQuant, 2014″ [reference 4], available online atthe following Internet address:“https://www.picoquant.com/images/uploads/page/files/7253/te chnotetcspc.pdf”, and also the work “D. V. O'Connor, D. Phillips, “TimeCorrelated Single Photon Counting”, Academic Press, New York, 1984,pages 25 to 34″ [reference 5].

The fluorescence quantum yield corresponds to the proportion ofluminescence photons emitted per amount of photons absorbed by thehybrid material. Preferably, its value is obtained according to anabsolute measurement method, namely not involving a third compound and acalibrating function. It is, for example, measured with an integratingsphere as module of a spectrofluorometer. For a measurement of theabsolute value, reference may be made to the document “Rohwer, L. S.,Martin, J. E.; “Measuring the absolute quantum efficiency of luminescentmaterials”, J. Lumin., 2005, 115, pages 77-90” [reference 6].

The value of the fluorescence quantum yield can also be obtainedaccording to a relative measurement method, the principle of which is asfollows: knowing the absolute fluorescence quantum yield of a thirdcompound, the value of the absolute measurement is obtained by a simplerule of three. For example, without an integrating sphere, thefluorescence quantum yield can be determined by relative measurement ofthe sample (a reference solution of quinine sulfate as third compoundis, for example, used in the document “Velapoli, R. A.; Mielenz, K. D.,“A Fluorescence Standard Reference Material: Quinine Sulfate Dihydrate”,Appl. Opt., 1981, 20, 1718” [reference 7] available online at thefollowing Internet address:https://www.nist.gov/sites/default/files/documents/srm/SP260-64.PDF).

Generally, the values obtained by the absolute and relative measurementmethod are identical or similar.

Advantageously, the additional primary fluorophore can have afluorescence emission spectrum, the centroid of which is at a wavelengthcomprised between 355 nm and 365 nm, typically centered at approximately360 nm, so that the interaction effect is optimum with the secondaryfluorophore.

The time-correlated single photon counting is a spectroscopy techniquewhich makes it possible to measure the fluorescence decay constant ofphotoluminescent compounds or their mixtures. It consists in exciting afluorophore or a fluorescent mixture by means of a rapidly decreasinglight beam (rapidly decreasing with respect to the luminescent radiationemitted in return to be observed), and in then observing, by means of amonochromator coupled to a photomultiplier, the photoluminescenceoutcome. The hybrid material of the invention is more particularlyexcited with a low frequency (typically up to 1 MHz) in order to preventany pile-up of scintillation pulses.

Preferentially, the additional primary fluorophore is chosen from atleast one compound such as:

-   -   an oxazole (such as, for example, 2,5-diphenyloxazole (PPO));        and/or    -   a polycyclic aromatic compound which is a hydrocarbon (namely        without heteroatom) comprising from 3 to 6 phenyl rings, at        least one phenyl ring of which optionally comprises at least one        substituent in the ortho, meta or preferably para position (for        example a linear or branched, preferably saturated, alkyl        substituent R preferably comprising from 1 to 10 carbon atoms,        preferentially from 1 to 4 carbon atoms), such as, for example,        para-terphenyl (pTP), meta-terphenyl (mTP), para-quaterphenyl,        biphenyl, 1-vinylbiphenyl, 2-vinylbiphenyl, 4-isopropylbiphenyl,        para-sexiphenyl or their mixtures; and/or    -   an oxadiazole, such as, for example,        2-phenyl-5-(4-biphenyl)-1,3,4-oxadiazole (PBD),        2-(4′-(t-butyl)phenyl)-5-(4″-biphenylyl)-1,3,4-oxadiazole        (Butyl-PBD) or their mixtures; and/or    -   a compound from the family of the anthracenes, such as        anthracene, 9-anthracenyl methacrylate or their mixtures; and/or    -   a naphthalene substituted by a vinyl group (such as        1-vinylnaphthalene or 2-vinylnaphthalene), a naphthalene        substituted by an R substituent as defined above (such as, for        example, 1-methylnaphthalene) or their mixtures; and/or    -   a carbazole, such as, for example, N-vinylcarbazole,        N-ethylcarbazole, N-(2-ethylhexyl)carbazole or their mixtures;        and/or    -   tetraphenylbutadiene.

More particularly, the additional primary fluorophore is2,5-diphenyloxazole (PPO), para-terphenyl (pTP), indeed evenmeta-terphenyl (mTP), or their mixtures.

As indicated above, the additional primary fluorophore can be covalentlybonded to the polymeric matrix, for example via the polymerization of avinyl, allyl, acrylic or methacrylic function carried by the additionalprimary fluorophore. By way of example, 1-vinylbiphenyl,2-vinylbiphenyl, 1-vinylnaphthalene, 2-vinylnaphthalene,1-methylnaphthalene or N-vinylcarbazole can be used for the purpose ofbeing covalently bonded in order to form a copolymer with a polymericmatrix.

The incorporated fluorescent mixture can further comprise a secondaryfluorophore. The secondary fluorophore further improves the detection ofthe radioluminescent radiation.

The concentration by weight of the secondary fluorophore with respect tothe weight of the hybrid material can be comprised between 0.002% and0.5% by weight, preferentially between 0.01% and 0.2% by weight, morepreferentially still between 0.01% and 0.1% by weight.

By way of example, the secondary fluorophore can be chosen from1,4-di[2-(5-phenyloxazolyl)]benzene, 1,4-bis(2-methylstyryl)benzene,1,4-bis(4-methyl-5-phenyl-2-oxazolyl)-benzene, 9,10-diphenylanthraceneor their mixtures. The polymeric matrix then comprises, with respect tothe weight of the hybrid material, from 0.002% by weight to 0.2% byweight of the secondary fluorophore.

According to a first embodiment, the secondary fluorophore can be chosenso that it has a light absorption spectrum and a fluorescence emissionspectrum, the centroid of which is respectively at a wavelengthcomprised between 330 nm and 380 nm and comprised between 405 nm and 460nm, and the fluorescence quantum yield of which in a nonpolar solvent iscomprised between 0.5 and 1. The secondary fluorophore can thus bechosen from 1,4-bis(5-phenyl-2-oxazolyl)benzene (POPOP),1,4-bis(4-methyl-5-phenyl-2-oxazolyl)benzene (dimethylPOPOP),bis-methylstyrylbenzene (bis-MSB), 9,10-diphenylanthracene (9,10-DPA) ortheir mixtures. The molecular structures of these secondary fluorophoresare illustrated below.

According to a second embodiment, the secondary fluorophore can bechosen so that it has a light absorption spectrum and a fluorescenceemission spectrum, the centroid of which is respectively at a wavelengthcomprised between 330 nm and 380 nm and comprised between 460 nm and 550nm, and the fluorescence quantum yield of which in a nonpolar solvent iscomprised between 0.5 and 1. The secondary fluorophore can then bechosen from coumarin 6, coumarin 7, coumarin 30, coumarin 102, coumarin151, coumarin 314, coumarin 334, 3-hydroxyflavone or their mixtures. Themolecular structures of these secondary fluorophores are illustratedbelow.

According to a third embodiment, the second fluorophore can be chosen sothat it has a light absorption spectrum and a fluorescence emissionspectrum, the centroid of which is respectively at a wavelengthcomprised between 330 nm and 380 nm and comprised between 550 nm and 630nm, and the fluorescence quantum yield of which in a nonpolar solvent iscomprised between 0.5 and 1. The secondary fluorophore can then bechosen from Nile red, rhodamine B or one of its salts,4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM),pyrromethene 580, any molecule of N-alkyl or N-alkyl orN-arylperylenediimide (such as, for example,N,N′-bis(2,5-di(tert-butyl)phenyl)-3,4,9,10-perylenedicarboximide). Themolecular structures of these secondary fluorophores are illustratedbelow.

The invention also relates to a process for the manufacture bypolymerization, via a polymerization medium, of the hybrid material ofthe invention which can be as defined in the present description, amongothers according to one or more of the alternative forms described forthis material.

The process for the manufacture of a hybrid material by polymerizationcomprises the following successive steps:

a) having available a polymerization medium comprising:

-   -   monomers, oligomers or their mixtures intended to form at least        one constituent polymer of the polymeric matrix which can be as        defined in the present description, among others according to        one or more of the alternative forms described for this        polymeric matrix;    -   a liquid fluorescent mixture comprising, in a molar        concentration with respect to the total number of moles of        primary fluorophore in the liquid fluorescent mixture, i) from        80 molar % (more specifically 80.0 molar %) to 99.6 molar % of a        main primary fluorophore consisting of naphthalene and ii) from        0.4 molar % to 20 molar % (more specifically 20.0 molar %) of an        additional primary fluorophore, the centroid of the light        absorption spectrum and of the fluorescence emission spectrum of        which have respectively a wavelength comprised between 250 nm        and 340 nm and comprised between 330 nm and 380 nm, the        fluorescence decay constant of which is comprised between 1 ns        and 10 ns, and the fluorescence quantum yield in a nonpolar        solvent of which is comprised between 0.2 and 1, preferentially        comprised between 0.5 and 1;

b) polymerizing the polymerization medium in order to obtain the hybridmaterial.

During step b) of polymerization of a precursor of the polymer (namely aprecursor such as the abovementioned monomers and/or oligomers), themain and additional primary fluorophores, as well as any other compoundpresent in the polymerization medium, are generally trapped anddistributed homogeneously in the polymeric matrix being formed.

Consequently, in the present description, the “liquid fluorescentmixture” is the fluorescent mixture comprising the main primaryfluorophore and the additional primary fluorophore and which iscontained in the polymerization medium before carrying out step b).

The “incorporated fluorescent mixture” denotes the fluorescent mixturecomprising the main primary fluorophore and the additional primaryfluorophore and which is incorporated in the hybrid material after thepolymerization step b), for example by grafting or dispersion.

The “fluorescent mixture for extrusion” denotes the fluorescent mixturecomprising the main primary fluorophore and the additional primaryfluorophore which is contained in the extrusion mixture furthermorecontaining polymerized ingredients intended to form a polymeric matrix.

The polymerization medium generally does not comprise a solvent. Themanufacturing process is then a “bulk polymerization” process.

Nevertheless, optionally, the polymerization medium can further comprisea polymerization solvent. The manufacturing process is then generallycarried out at reflux of the solvent. The solvent of the polymerizationmedium can be chosen from xylene, chloroform, dichloromethane,chlorobenzene, benzene, tetrachloromethane or their mixtures.

The monomers or the oligomers can comprise at least one aromatic,(meth)acrylic or vinyl group. At least one monomer can be chosen fromstyrene, vinyltoluene, vinylxylene, 1-vinylbiphenyl, 2-vinylbiphenyl,1-vinylnaphthalene, 2-vinylnaphthalene, 1-methylnaphthalene,N-vinylcarbazole, methyl (meth)acrylate, (meth)acrylic acid or2-hydroxyethyl (meth)acrylate.

The polymerization medium can for its part comprise from 1% by weight to25% by weight (indeed even from 1% by weight to 5% by weight) of theliquid fluorescent mixture.

The liquid fluorescent mixture can comprise from 90 molar % (morespecifically 90.0 molar %) to 99.1 molar % (indeed even from 96 molar %(more specifically 96.0 molar %) to 99.1 molar %) of the main primaryfluorophore; indeed even i) from 95.6 molar % to 99.1 molar % of themain primary fluorophore consisting of naphthalene and ii) from 0.9molar % to 4.4 molar % of the additional primary fluorophore.

The polymerization medium can further comprise at least one chemicalentity intended to be incorporated in the hybrid material in order toconfer on it or to improve specific properties (for example a secondaryfluorophore) and/or at least one entity intended to be consumed ormodified during the polymerization step b) (for example a crosslinkingagent, a polymerization initiator).

The polymerization medium can comprise:

-   -   a secondary fluorophore, typically according to a concentration        by weight comprised between 0.002% and 0.5% by weight, indeed        even from 0.002% by weight to 0.2% by weight; and/or    -   a crosslinking agent, typically according to a concentration by        weight comprised between 0.1% and 20% (more specifically 20.0%)        by weight, indeed even from 0.001% by weight to 1% by weight;        and/or    -   a polymerization initiator, typically according to a        concentration from 0.001% by weight to 1% by weight.

The additional primary fluorophore, the secondary fluorophore and/or thecrosslinking agent can also be as defined according to one or more ofthe alternative forms described in the present description.

The polymerization reaction according to step b) can be carried outaccording to the conditions ordinarily employed by a person skilled inthe art.

Thus, it can be started with a polymerization initiator, among others aphotoinitiator, in order to initiate a radical polymerization.Preferably, the photoinitiator is not a photoinitiator which can beactivated under UV radiation, such as, for example, TPO. A UVphotoinitiator can produce residual compounds or modify other compoundsof the plastic scintillation material, which results in a photobleachingof this material harmful to a good scintillation yield.

Preferably, in order to as much as possible avoid such a problem, thephotoinitiator used in the invention can be activated under visiblelight radiation. For example, as indicated in the patent application WO2013076281 [reference 8], the polymerization initiator can be chosenfrom a peroxide compound (for example benzoyl peroxide), a nitrilecompound (for example azo(bis)isobutyronitrile (AIBN)) or theirmixtures.

When the polymerization reaction is carried out, among others, withmethacrylate monomers, it can be induced by heating the polymerizationmedium to a suitable temperature (generally comprised between 40° C. and140° C.), or by doping the polymerization medium with2,2-dimethoxy-2-phenylacetophenone as polymerization initiator and bythen carrying out irradiation under UV (for example at a wavelength of355 nm). The polymerization reaction in the presence of styrene monomerscan be induced thermally, typically by heating between 40° C. and 140°C.

The process for the manufacture of the hybrid material by polymerizationof the invention can be such that, during the polymerization step b),the polymerization medium is heated to a polymerization temperaturecomprised between 100° C. and 140° C. (for a period of time sufficientfor the polymerization to be complete, generally for 24 hours) and thencooled according to a rate of 10° C. to 20° C. per day (generally inorder to reach ambient temperature, typically 20° C.) until the hybridmaterial is obtained.

For example, the polymerization medium can be heated at 140° C. for 24hours and then cooled according to a rate of 20° C. per day until it hasreturned to 20° C.

Steps a) and b) of the process for manufacture by polymerization via apolymerization medium of the invention can be carried out in a mold inorder to obtain a part as defined in the present description or apreform of this part.

The process of manufacture of the invention by polymerization via apolymerization medium can further comprise a step c) during which thehybrid material or the preform of the part is machined in order toobtain the part as defined in the present description. This machiningstep consists, for example, in precision grinding the faces (for exampleon a lathe) and in then polishing them.

The invention also relates to a hybrid material obtained or obtainableby the process for manufacture by polymerization of a hybrid materialvia a polymerization medium, among others according to one or more ofthe alternative forms described for this process.

The invention also relates to a part for plastic scintillation detectioncomprising a hybrid material which can be as defined according to one ormore of the alternative forms described in the present description forthis material.

Generally, the part for plastic scintillation detection is thuscomposed, completely or partially, of a hybrid material comprising:

-   -   a polymeric matrix; and    -   a fluorescent mixture incorporated in the polymeric matrix and        comprising, in a molar concentration with respect to the total        number of moles of primary fluorophore in the incorporated        fluorescent mixture, i) from 80 molar % (more specifically 80.0        molar %) to 99.6 molar % of a main primary fluorophore        consisting of naphthalene and ii) from 0.4 molar % to 20 molar %        (more specifically 20.0 molar %) of an additional primary        fluorophore, the centroid of the luminous absorption spectrum        and of the fluorescence emission spectrum of which respectively        have a wavelength comprised between 250 nm and 340 nm and        comprised between 330 nm and 380 nm (indeed even between 355 nm        and 365 nm), the fluorescence decay constant of which is        comprised between 1 ns and 10 ns and the fluorescence quantum        yield in a nonpolar solvent of which is comprised between 0.2        and 1 (indeed even between 0.5 and 1). This part can be a unit        (such as, for example, an optical fiber) or a subunit of a        device for plastic scintillation detection (for example the        hybrid compartment of a detector of phoswich type).

The polymeric matrix of the hybrid material composing all or a portionof the part can be composed, completely or partially, of at least onepolymer comprising repeat units resulting from the polymerization ofmonomers comprising at least one aromatic, (meth)acrylic or vinyl groupand/or it can be constituted, completely or partially, of at least onecrosslinked polymer.

At least monomer intended to form the polymeric matrix is chosen fromstyrene, vinyltoluene, vinylxylene, 1-vinylbiphenyl, 2-vinylbiphenyl,1-vinylnaphthalene, 2-vinylnaphthalene, 1-methylnaphthalene,N-vinylcarbazole, methyl (meth)acrylate, (meth)acrylic acid or2-hydroxyethyl (meth)acrylate. Preferably, the monomer is styrene orvinyltoluene.

The part for plastic scintillation detection of the invention can beprovided according to the following alternative forms, which areoptionally combined:

-   -   the hybrid material comprises from 1% by weight to 25% by weight        (indeed even from 1% by weight to 5% by weight) of the        incorporated fluorescent mixture, and/or;    -   the incorporated fluorescent mixture comprises i) from 90 molar        % (more specifically 90.0 molar %) to 99.1 molar % (indeed even        from 96 molar % (more specifically 96.0 molar %) to 99.1 molar        %) of the main primary fluorophore, indeed even comprises from        95.6 molar % to 99.1 molar % of the main primary fluorophore        consisting of naphthalene, and ii) from 0.9 molar % to 4.4 molar        % of the additional primary fluorophore;    -   the additional primary fluorophore is covalently bonded to the        polymeric matrix, and/or;    -   the additional primary fluorophore is chosen from        2,5-diphenyloxazole (PPO), para-terphenyl (pTP), meta-terphenyl        (mTP), biphenyl, 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole        (PBD), 2-(4′-(t-butyl)phenyl)-5-(4″-biphenylyl)-1,3,4-oxadiazole        (Butyl-PBD), anthracene, para-quaterphenyl,        tetraphenylbutadiene, N-ethylcarbazole, hexyl)carbazole,        4-isopropylbiphenyl, para-sexiphenyl, 1-vinylbiphenyl,        2-vinylbiphenyl, 1-vinylnaphthalene, 2-vinylnaphthalene,        1-methylnaphthalene, N-vinylcarbazole, 9-anthracenyl        methacrylate or their mixtures; the additional primary        fluorophore preferably being 2,5-diphenyloxazole (PPO),        para-terphenyl (pTP), indeed even meta-terphenyl (mTP), or their        mixtures.

The incorporated fluorescent mixture of the hybrid material of the partcan further comprise a secondary fluorophore, for example at aconcentration by weight, with respect to the weight of the hybridmaterial, which is comprised between 0.002% and 0.5% by weight, indeedeven from 0.01% by weight to 0.2% by weight, of the secondaryfluorophore.

The primary fluorophore can be chosen from1,4-di[2-(5-phenyloxazolyl)]benzene, 1,4-bis(2-methylstyryl)benzene,1,4-bis(4-methyl-5-phenyl-2-oxazolyl)benzene, 9,10-diphenyl-anthraceneor their mixtures.

According to a first embodiment, the secondary fluoro-phore has a lightabsorption spectrum and a fluorescence emission spectrum, the centroidof which is respectively at a wavelength comprised between 330 nm and380 nm and comprised between 405 nm and 460 nm, and the fluorescencequantum yield in a nonpolar solvent of which is comprised between 0.5and 1.

In this case, the secondary fluorophore can be chosen from1,4-bis(5-phenyl-2-oxazolyl)benzene (POPOP),1,4-bis(4-methyl-5-phenyl-2-oxazolyl)benzene (dimethylPOPOP),bis-methylstyrylbenzene (bis-MSB), 9,10-diphenylanthracene (9,10-DPA) ortheir mixtures.

According to a second embodiment, the secondary fluorophore has a lightabsorption spectrum and a fluorescence emission spectrum, the centroidof which is respectively at a wavelength comprised between 330 nm and380 nm and comprised between 460 nm and 550 nm, and the fluorescencequantum yield in a nonpolar solvent of which is comprised between 0.5and 1.

In this case, the secondary fluorophore can be chosen from coumarin 6,coumarin 7, coumarin 30, coumarin 102, coumarin 151 coumarin 314,coumarin 334, 3-hydroxyflavone or their mixtures.

According to a third embodiment, the secondary fluorophore has a lightabsorption spectrum and a fluorescence emission spectrum, the centroidof which is respectively at a wavelength comprised between 330 nm and380 nm and comprised between 550 nm and 630 nm, and the fluorescencequantum yield in a nonpolar solvent of which is comprised between 0.5and 1.

In this case, the secondary fluorophore can be chosen from Nile red,rhodamine B or one of its salts,4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran,pyrromethene 580 or an N-alkyl- or N-aryl-perylenediimide.

Because of the possibility of varying the relative proportion betweenthe main primary fluorophore and the additional primary fluorophore, thehybrid material (and thus the part for plastic scintillation detection)can have a fluorescence decay constant comprised between 10 ns and 90 ns(indeed even between 15 ns and 80 ns); particularly between 25 ns and 75ns, more particularly between 28 ns and 70 ns.

The part can have a great variety of shapes, for example aparallelepipedal or cylindrical shape.

The part of parallelepipedal shape is, for example, a plasticscintillator compartment capable of being incorporated in a device forplastic scintillation detection.

When the part has a cylindrical shape, and participates, for example, inthe composition of a plastic scintillator pillar, it can have a squareor rectangular section.

When the part of cylindrical shape is, for example, a scintillatingoptical fiber (in which case the hybrid material comprises a polymericmatrix constituted, completely or partially of at least one polymerwhich is not crosslinked), it can have a circular, elliptical orhexagonal section.

An optical fiber is a wave guide which makes use of the refractiveproperties of light. It is generally constituted of a core surrounded bya sheath. The core of the fiber has a slightly higher refractive index(difference of a few thousandths) than the sheath. The light is thuscompletely reflected multiple times at the interface between thematerial of the internal fiber constituting the core and the sheathingmaterial by total internal reflection.

The scintillating optical fiber as part of the invention 10 can comprisea polymer fiber 11 composed, completely or partially, of the hybridmaterial and provided or not provided with a sheath 12 covering thepolymer fiber and composed, completely or partially, of a sheathingmaterial for an optical fiber, the refractive index of which is lessthan that of the hybrid material, the hybrid material comprising apolymeric matrix constituted, completely or partially, of at least onepolymer which is not crosslinked.

Several scintillating optical fibers can be combined to give a bundle offibers.

The presence of a sheath is not obligatory. For example, when the aim ofthe part is to detect an alpha particle, the scintillating optical fiberis composed solely of a polymer internal fiber devoid of a sheath inorder to prevent the energy of the incident radiation from being largelyabsorbed by the sheath.

Nevertheless, generally, the scintillating optical fiber comprises asheath, the sheathing material of which is a material ordinarily usedfor an optical fiber, in particular a scintillating optical fiber. Forexample, the sheathing material is chosen from poly(methylmethacrylate), poly(benzyl methacrylate), poly(trifluoromethylmethacrylate), poly(trifluoroethyl methacrylate) or their mixtures.

The invention also relates to a process for the manufacture by extrusionof a part for plastic scintillation detection and composed, completelyor partially, of a hybrid material, it being possible for the part to beas defined according to one or more of the alternative forms describedin the present description, the process comprising the followingsuccessive steps:

a′) having available an extrusion mixture comprising:

-   -   polymerized ingredients intended to form a polymeric matrix as        defined in the present description, among others according to        one or more of the alternative forms described, with the        exception of the case where the polymeric matrix is constituted,        completely or partially (preferably more than 10% by weight of        polymer in the polymeric matrix), of at least one crosslinked        polymer;    -   a fluorescent mixture for extrusion comprising, in a molar        concentration with respect to the total number of moles of        primary fluorophore in the fluorescent mixture for extrusion:

i) from 80 molar % (more specifically 80.0 molar %) to 99.6 molar %(indeed even from 90 molar % (more specifically 90.0 molar %) to 99.1molar %, indeed even from 96 molar % (more specifically 96.0 molar %) to99.1 molar %) of a main primary fluorophore consisting of naphthalene;and

ii) from 0.4 molar % to 20 molar % (more specifically 20.0 molar %) ofan additional primary fluorophore, the centroid of the light absorptionspectrum and of the fluorescence emission spectrum of which respectivelyhave a wavelength comprised between 250 nm and 340 nm and comprisedbetween 330 nm and 380 nm, the fluorescence decay constant of which iscomprised between 1 ns and 10 ns and the fluorescence quantum yield in anonpolar solvent of which is comprised between 0.2 and 1;

b′) under an extrusion atmosphere at an extrusion temperature comprisedbetween 170° C. and 200° C., extruding the extrusion mixture through adie in order to obtain the part composed, completely or partially, of ahybrid material.

The fluorescent mixture for extrusion can also comprise i) from 95.6molar % to 99.1 molar % of the main primary fluorophore consisting ofnaphthalene and ii) from 0.9 molar % to 4.4 molar % of the additionalprimary fluorophore.

A process for manufacture by extrusion is essentially a process for thetransformation of polymerized ingredients which, once softened or in themolten state by virtue of heat, are forced continuously through a diewhich gives it geometry to the polymer-base profiled element obtained onconclusion of the process. The extrusion process is well known to aperson skilled in the art: it is described, for example, in the document“Techniques de 1'ingenieur, Extrusion extrusion monovis (partie 1),Reference AM3650, publication de 2002” [Techniques of the Engineer,Extrusion—single-screw extrusion (part 1), Reference AM3650, publicationof 2002] [reference 9].

The polymerized ingredients which can be used are formed from one ormore polymers which exhibit a thermal stability such that the polymer isnot degraded at the temperature required for the extrusion, whichdepends on the glass transition temperature. Their chemical compositionis identical to that of the polymeric matrix.

The polymerized ingredients are generally in the solid form, inparticular in the form of granules.

The extrusion step b′) can be carried out by means of an extruder (forexample an extruder of single-screw, twin-screw or multiscrew type) orof a cokneader. Typically, the die is positioned at the outlet of theextruder.

The extrusion atmosphere can be chemically inert with regard to theextrusion mixture. Such an atmosphere limits or prevents the oxidationof the polymeric matrix obtained. It comprises, for example, nitrogen ora rare gas, such as, for example, argon.

Typically, the extrusion process of the invention is carried out at anextrusion temperature of less than 218° C., which is the evaporationtemperature of naphthalene at atmospheric pressure, but at a temperaturesufficiently high to soften or melt the polymerized ingredients, forexample at an extrusion temperature comprised between 170° C. and 200°C.

The invention also relates to a process for the manufacture bypolymerization of a part for plastic scintillation detection andcomposed, completely or partially, of a hybrid material, it beingpossible for the part to be as defined according to one or more of thealternative forms described in the present description, the processcomprising at least one polymerization via a polymerization mediumaccording to the following successive steps:

a) in a first mold, having available a first polymerization mediumcomprising:

-   -   monomers, oligomers or their mixtures intended to form at least        one constituent polymer of a polymeric matrix as defined        according to one or more of the alternative forms described in        the present description (among others, the case where the        polymeric matrix is constituted, completely or partially, of at        least one crosslinked polymer);    -   a liquid fluorescent mixture comprising, in a molar        concentration with respect to the total number of moles of        primary fluorophore in the liquid fluorescent mixture:

i) from 80 molar % (more specifically 80.0 molar %) to 99.6 molar % of amain primary fluorophore consisting of naphthalene; and

ii) from 0.4 molar % to 20 molar % (more specifically 20.0 molar %) ofan additional primary fluorophore, the centroid of the light absorptionspectrum and of the fluorescence emission spectrum of which respectivelyhave a wavelength comprised between 250 nm and 340 nm and comprisedbetween 330 nm and 380 nm, the fluorescence decay constant of which iscomprised between 1 ns and 10 ns, and the fluorescence quantum yield ina nonpolar solvent of which is comprised between 0.2 and 1;

b) polymerizing the first polymerization medium in order to directlyobtain the part or a preform of the part which is subsequently modified(for example machined, among others by drawing the preform) in order toobtain the part.

In the process for the manufacture of a part by polymerization, thefluorescent mixture is liquid as it is mixed in the first polymerizationmedium with monomers and/or oligomers.

The internal volume of the mold can have a parallelepipedal orcylindrical shape. The cylindrical shape can be of circular, elliptical,hexagonal, square or rectangular section.

When the internal volume of the mold has a parallelepipedal shape, theprocess for manufacture by polymerization can so that the part ofparallelepipedal shape obtained on conclusion of step b) is a plasticscintillator compartment as defined in the present description andcapable of being incorporated in a device for plastic scintillationdetection.

In this case, the plastic scintillator compartment of parallelepipedalshape can be obtained directly on conclusion of the process formanufacture by polymerization, after, if appropriate, an optionalprecision grinding step.

When the internal volume of the mold has a cylindrical shape, theprocess for manufacture by polymerization can be such that the part is ascintillating optical fiber 10 devoid of the sheath which can be asdefined in the present description according to one or more of itsalternative forms, so that a cylindrical bar as preform of the part isobtained on conclusion of step b), the process comprising the followingadditional step carried out after the polymerization step b):

c) in a fiber-drawing tower, softening by heating and then drawing thepreform of the part in order to obtain a polymer fiber 11 composed,completely or partially, of the hybrid material as scintillating opticalfiber 10 devoid of a sheath.

Alternatively, when the internal volume of the mold has a cylindricalshape, the process for manufacture by polymerization can be such thatthe part is a scintillating optical fiber 10 provided with a sheath 12which can be as defined in the present description according to one ormore of the alternative forms, so that a cylindrical bar as firstpreform of the part is obtained on conclusion of step b), the processcomprising the following additional step carried out after step b):

-   -   b1) placing the first preform of the part in a second        cylindrical mold and then filling the free volume delimited by        the internal face of the second cylindrical mold and the        external face of the first preform of the part with a second        polymerization medium comprising a precursor of a sheathing        material for optical fiber for which the refractive index of the        sheathing material is less than that of the hybrid material;    -   b2) polymerizing the second polymerization medium in order to        form the sheathing material which covers the first preform of        the part, in order to obtain a second preform of the part        (constituting a parison);

c) in a fiber-drawing tower, softening by heating and then drawing thesecond preform of the part in order to obtain, as scintillating opticalfiber 10 provided with a sheath 12, a polymer fiber 11 composed,completely or partially, of the hybrid material and provided with thesheath 12 covering the polymer fiber 11.

In these two alternatives, the internal volume of the cylindrical moldhas, for example, a circular section. The mold can then have an internaldiameter comprised between 2 cm and 10 cm (typically 5 cm) and/or alongitudinal length comprised between 10 cm and 100 cm (typically 50cm). These dimensions correspond generally to those of the cylindricalbar as parison or preform of the part.

The precursor of the sheathing material is, for example, chosen frommethyl methacrylate, benzyl methacrylate, trifluoromethyl methacrylate,trifluoroethyl methacrylate or their mixtures.

The preform of the part or parison is generally placed vertically overthe fiber-drawing tower. On conclusion of step c), the scintillatingoptical fiber, provided or not provided with a sheath, is generallyrecovered by gravimetric tower fiber drawing.

During the polymerization step b) and/or b1), the first polymerizationmedium can be heated to a first polymerization temperature comprisedbetween 100° C. and 140° C. (for example for a period of time of 12 h to24 h, among others one day at 140° C.) and then cooled according to afall in the polymerization temperature of 10° C. to 20° C. per day untilthe part or the preform of the part is obtained. The cooling isgenerally continued until the ambient temperature of 20° C. is reached.

During the polymerization step b2), the second polymerization medium canbe heated to a second polymerization temperature comprised between 50°C. and 70° C. (for example for a period of time of 8 to 10 days, amongothers 10 days at 60° C.) and then cooled according to a fall in thepolymerization temperature of 10° C. to 20° C. per day until the part orthe preform of the part is obtained. The cooling is generally continueduntil the ambient temperature of 25° C. is reached.

The heating operation in order to soften can for its part be carried outduring step c) at a temperature comprised between 150° C. and 190° C.

The preform of the part can be precision ground immediately beforecarrying out the drawing step c). For example, the cylindrical bar isprecision ground by cutting its upper and lower part over a shortlength. The upper face of a part of parallelepipedal shape, namely theface which ends up in light contact with the ambient air, can also beprecision ground by cutting the upper part over a short length and thenpolishing.

On conclusion of the process for manufacture of polymerization, thescintillating optical fiber can be such that:

-   -   the diameter of the polymer fiber 11 is comprised between 50 μm        and 1 mm, and/or;    -   the thickness of the sheath 12 is comprised between 1 μm and 20        μm, and/or;    -   the length of the scintillating optical fiber is comprised        between 0.1 and 2 km.

The first polymerization medium and/or the second polymerization mediumcan comprise a polymerization solvent chosen, for example, from xylene,chloroform, dichloro-methane, chlorobenzene, benzene, tetrachloromethaneor their mixtures.

Regarding respectively the process for the manufacture of a part byextrusion or the process for the manufacture of a part bypolymerization, the fluorescent mixture for extrusion or the liquidfluorescent mixture can be such that:

-   -   it comprises from 90 molar % (more specifically 90.0 molar %) to        99.1 molar % (indeed even from 96 molar % (more specifically        96.0 molar %) to 99.1 molar %) of the main primary fluorophore,        and/or; indeed even i) from 95.6 molar % to 99.1 molar % of the        main primary fluorophore consisting of naphthalene and thus ii)        from 0.9 molar % to 4.4 molar % of the additional primary        fluorophore;    -   the additional primary fluorophore has a fluorescence quantum        yield in a nonpolar solvent comprised between 0.5 and 1, and/or;    -   it comprises a secondary fluorophore as defined in the present        description, among others according to one or more of the        alternative forms described.

The invention also relates to a device for plastic scintillationdetection comprising a part for plastic scintillation detection (whichcan be as defined according to one or more of the alternative formsdescribed in the present description) as hybrid plastic scintillatorelement, the part generally being composed, completely or partially, ofa hybrid material comprising:

-   -   a polymeric matrix; and    -   a fluorescent mixture incorporated in the polymeric matrix and        comprising, in a molar concentration with respect to the total        number of moles of primary fluorophore in the incorporated        fluorescent mixture:

i) from 80 molar % (more specifically 80.0 molar %) to 99.6 molar % of amain primary fluorophore consisting of naphthalene; and

ii) from 0.4 molar % to 20 molar % (more specifically 20.0 molar %) ofan additional primary fluorophore, the centroid of the light absorptionspectrum and of the fluorescence emission spectrum of which respectivelyhave a wavelength comprised between 250 nm and 340 nm and comprisedbetween 330 nm and 380 nm, the fluorescence decay constant of which iscomprised between 1 ns and 10 ns and the fluorescence quantum yield in anonpolar solvent of which is comprised between 0.2 and 1 (indeed evenbetween 0.5 and 1); the part being coupled to an electronic acquisitionmodule so that the module is capable of collecting the radioluminescentradiation emitted by the part when the latter is brought into contactwith an ionizing radiation or an ionizing particle.

The polymeric matrix of the hybrid material composing all or a portionof the part can be composed, completely or partially, of at least onepolymer comprising repeat units resulting from the polymerization ofmonomers comprising at least one aromatic, (meth)acrylic or vinyl groupand/or it can be constituted, completely or partially, of at least onecrosslinked polymer.

At least one monomer intended to form the polymeric matrix can be chosenfrom styrene, vinyltoluene, vinylxylene, 1-vinylbiphenyl,2-vinylbiphenyl, 1-vinylnaphthalene, 2-vinylnaphthalene,1-methylnaphthalene, N-vinylcarbazole, methyl (meth)acrylate,(meth)acrylic acid or 2-hydroxyethyl (meth)acrylate. Preferably, themonomer is styrene or vinyltoluene.

The hybrid material composing all or a portion of the part integrated inthe device for plastic scintillation detection of the invention can beprovided according to the following alternative forms, which areoptionally combined:

-   -   the hybrid material comprises from 1% by weight to 25% by weight        (indeed even from 1% by weight to 5% by weight) of the        incorporated fluorescent mixture, and/or;    -   the incorporated fluorescent mixture comprises from 90 molar %        (more specifically 90.0 molar %) to 99.1 molar % (indeed even        from 96 molar % (more specifically 96.0 molar %) to 99.1 molar        %) of the main primary fluorophore; indeed even i) from 95.6        molar % to 99.1 molar % of the main primary fluorophore        consisting of naphthalene and ii) from 0.9 molar % to 4.4 molar        % of the additional primary fluorophore, and/or;    -   the additional primary fluorophore is covalently bonded to the        polymeric matrix, and/or;    -   the additional primary fluorophore is chosen from        2,5-diphenyloxazole (PPO), para-terphenyl (pTP), meta-terphenyl        (mTP), biphenyl, 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole        (PBD), 2-(4′-(t-butyl)phenyl)-5-(4″-biphenylyl)-1,3,4-oxadiazole        (Butyl-PBD), anthracene, para-quaterphenyl,        tetraphenylbutadiene, N-ethylcarbazole, hexyl)carbazole,        4-isopropylbiphenyl, para-sexiphenyl, 1-vinylbiphenyl,        2-vinylbiphenyl, 1-vinylnaphthalene, 2-vinylnaphthalene,        1-methylnaphthalene, N-vinylcarbazole, 9-anthracenyl        methacrylate or their mixtures; the additional primary        fluorophore preferably being 2,5-diphenyloxazole (PPO),        para-terphenyl (pTP), indeed even meta-terphenyl (mTP), or their        mixtures.

The incorporated fluorescent mixture of the hybrid material of the partcan further comprise a secondary fluorophore, for example at aconcentration by weight with respect to the weight of the hybridmaterial which is comprised between 0.002% and 0.5% by weight, indeedeven from 0.01% by weight to 0.2% by weight, of the secondaryfluorophore.

The primary fluorophore can be chosen from1,4-di[2-(5-phenyloxazolyl)]benzene, 1,4-bis(2-methylstyryl)benzene,1,4-bis(4-methyl-5-phenyl-2-oxazolyl)benzene, 9,10-diphenyl-anthraceneor their mixtures.

According to a first embodiment, the secondary fluoro-phore has a lightabsorption spectrum and a fluorescence emission spectrum, the centroidof which is respectively at a wavelength comprised between 330 nm and380 nm and comprised between 405 nm and 460 nm, and the fluorescencequantum yield in a nonpolar solvent of which is comprised between 0.5and 1.

In this case, the secondary fluorophore can be chosen from1,4-bis(5-phenyl-2-oxazolyl)benzene (POPOP),1,4-bis(4-methyl-5-phenyl-2-oxazolyl)benzene (dimethylPOPOP),bis-methylstyrylbenzene (bis-MSB), 9,10-diphenylanthracene (9,10-DPA) ortheir mixtures.

According to a second embodiment, the secondary fluorophore has a lightabsorption spectrum and a fluorescence emission spectrum, the centroidof which is respectively at a wavelength comprised between 330 nm and380 nm and comprised between 460 nm and 550 nm, and the fluorescencequantum yield in a nonpolar solvent of which is comprised between 0.5and 1.

In this case, the secondary fluorophore can be chosen from coumarin 6,coumarin 7, coumarin 30, coumarin 102, coumarin 151 coumarin 314,coumarin 334, 3-hydroxyflavone or their mixtures.

According to a third embodiment, the secondary fluorophore has a lightabsorption spectrum and a fluorescence emission spectrum, the centroidof which is respective at a wavelength comprised between 330 nm and 380nm and comprised between 550 nm and 630 nm, and the fluorescence quantumyield in a nonpolar solvent of which is comprised between 0.5 and 1.

In this case, the secondary fluorophore can be chosen from Nile red,rhodamine B or one of its salts,4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran,pyrromethene 580 or an N-alkyl- or N-aryl-perylenediimide.

Because of the possibility of varying the relative proportion betweenthe main primary fluorophore and the additional primary fluorophore, thehybrid material (and thus the part for plastic scintillation detectionand the device which integrates it) can have a fluorescence decayconstant comprised between 10 ns and 90 ns (indeed even between 15 nsand 80 ns); particularly between 25 ns and 75 ns, more particularlybetween 28 ns and 70 ns.

The part of the device can have a great variety of shapes, for example aparallelepipedal or cylindrical shape.

The part of parallelepipedal shape is, for example, a plasticscintillator compartment capable of being incorporated in a device forplastic scintillation detection.

When the part has a cylindrical shape, and participates, for example, inthe composition of a plastic scintillator pillar, it can have a squareor rectangular section.

When the part of cylindrical shape is, for example, a scintillatingoptical fiber (in which case the hybrid material comprises a polymericmatrix constituted, completely or partially of at least one polymerwhich is not crosslinked), it can have a circular, elliptical orhexagonal section.

The scintillating optical fiber as part of the invention 10 can comprisea polymer fiber 11 composed, completely or partially, of the hybridmaterial and provided or not provided with a sheath 12 covering thepolymer fiber and composed, completely or partially, of a sheathingmaterial for an optical fiber, the refractive index of which is lessthan that of the hybrid material, the hybrid material comprising apolymeric matrix constituted, completely or partially, of at least onepolymer which is not crosslinked.

Several scintillating optical fibers can be combined to give a bundle offibers.

The presence of a sheath is not obligatory. For example, when the aim ofthe part is to detect an alpha particle, the scintillating optical fiberis composed solely of a polymer internal fiber devoid of a sheath inorder to prevent the energy of the incident radiation from being largelyabsorbed by the sheath.

Nevertheless, generally, the scintillating optical fiber comprises asheath, the sheathing material of which is a material ordinarily usedfor an optical fiber, in particular a scintillating optical fiber. Forexample, the sheathing material is chosen from poly(methylmethacrylate), poly(benzyl methacrylate), poly(trifluoromethylmethacrylate), poly(trifluoroethyl methacrylate) or their mixtures.

The coupling between the part as plastic scintillator element and theacquisition module is generally carried out by bringing the acquisitionmodule into contact with a portion of the part from which theradioluminescent radiation emerges from the part.

According to a first embodiment, the device for plastic scintillationdetection is such that the hybrid plastic scintillator element is afirst hybrid plastic scintillator element 1, the device furthercomprising a second fast plastic scintillator element 2, thefluorescence decay constant of which is less than that of the firsthybrid plastic scintillator element 1, these plastic scintillatorelements 1 and 2 forming a plastic scintillator assembly. The firsthybrid plastic scintillator element 1 is preferably composed, completelyor partially, of a hybrid material, the fluorescence decay constant ofwhich is comprised within one of the abovementioned ranges for thehybrid material (for example between 10 ns and 90 ns, indeed evencomprised between 15 ns and 80 ns, advantageously comprised between 30ns and 80 ns, particularly between 70 ns and 80 ns; or between 25 ns and75 ns, indeed even between 28 ns and 70 ns, when the molar concentrationof the main primary fluorophore consisting of naphthalene is comprisedbetween 95.6% and 99.1%). The device is preferentially a device ofphoswich type, in which, for example, each plastic scintillator elementis a plastic scintillator compartment.

However, the invention described is not limited to the incorporation ofthe hybrid material in a plastic scintillator detector of phoswich type.It is advantageous so long as a person skilled in the art needs aplastic scintillator with a predetermined and optimized fluorescencedecay constant.

The first hybrid plastic scintillator element 1 can be in direct contactwith the second fast plastic scintillator element 2.

According to another alternative, the first hybrid plastic scintillatorelement 1 is in contact with the second fast plastic scintillatorelement 2 via a bonding layer 5. The plastic scintillator assembly thusfurther comprises a bonding layer.

In the case where the plastic scintillator elements are ofparallelepipedal shape, the first hybrid plastic scintillator elementand the second fast plastic scintillator element are typically incontact with one another via one of their faces, preferably their faceof greatest surface area or of identical surface area.

In the case where the plastic scintillator elements are of cylindricalshape, the first hybrid plastic scintillator element and the second fastplastic scintillator element are typically in contact with one anothervia their circular faces, which generally have identical surface areasat the points of their contact.

Taking as reference the direction R of propagation of the ionizingradiation or of the ionizing particle with regard to the device forplastic scintillation detection, the first hybrid plastic scintillatorelement can be without distinction the upstream plastic scintillatorelement or the downstream plastic scintillator element, in which casethe second fast plastic scintillator element is respectively thedownstream or upstream plastic scintillator element.

With reference to the direction of propagation of the ionizing radiationor of the ionizing particle with regard to the device, the first hybridplastic scintillator element 1 is preferably the upstream plasticscintillator element and the second fast plastic scintillator element 2is the downstream plastic scintillator element.

The plastic scintillator elements 1 and 2 can have differentthicknesses, so that the device comprises a thin plastic scintillatorelement and a thick plastic scintillator element. Both configurationsare thus possible: the first hybrid plastic scintillator element can bethe thin plastic scintillator element or the thick plastic scintillatorelement.

Preferably, the thickness of the first hybrid plastic scintillatorelement is less than that of the second fast plastic scintillatorelement. Thus, according to a preferential embodiment of the inventionfor the purpose of promoting beta/gamma discrimination, the device cancomprise a thin first hybrid plastic scintillator element 1 and a thicksecond fast plastic scintillator element 2. Preferably, the device thencomprises the first thin hybrid plastic scintillator element 1 upstreamand the second thick fast plastic scintillator element 2 downstream,with reference to the direction R of propagation of the ionizingradiation or of the ionizing particle with regard to the device.

The thin plastic scintillator element can have a thickness from 10 μm to1 mm, for example from 50 μm to 1 mm, preferably from 100 μm to 500 μm;and the thick plastic scintillator element can have a thickness rangingfrom 1 mm to several centimeters, for example from 1 mm to 10 cm,preferably from 3 mm to 5 cm.

The second fast plastic scintillator element 2 can have a fluorescencedecay constant comprised between 1 ns and 7 ns.

The second fast plastic scintillator element 2 can comprise a polymericmatrix which can be as defined in the present description, among othersaccording to one or more of the alternative forms described for thispolymeric matrix, and/or a fast primary fluorophore chosen from2,5-diphenyloxazole (PPO), para-terphenyl (pTP), meta-terphenyl (mTP),biphenyl, 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD),2-(4′-(t-butyl)phenyl)-5-(4″-biphenylyl)-1,3,4-oxadiazole (butyl-PBD),anthracene or their mixtures. Preferably, the fast primary fluorophoreis 2,5-diphenyl-oxazole (PPO), para-terphenyl (pTP), indeed evenmeta-terphenyl (mTP), or their mixtures.

The second fast plastic scintillator element 2 can comprise a secondaryfluorophore which can be as defined in the present description, amongothers according to one or more of the alternative forms described.

According to a second embodiment, the device for plastic scintillationdetection according to the invention can comprise a single hybridplastic scintillator element (“single-compartment” plastic scintillationdevice). Such a single-compartment device is advantageous when it iscoupled to an electronic acquisition module, the sampling frequency ofwhich is less than 250 MHz: in accordance with the Niquist-Shannontheorem, a long pulse, such as obtained with a single hybrid plasticscintillator, is better described with such an acquisition module forwhich the electronics are limited in number of points per nanosecond.

Generally, whatever the embodiment, the part can be coupled to theelectronic acquisition module by an optical interface layer 6, namely byoptical coupling.

The optical interface layer has, among others, the property of allowingthe passage of the radiation exiting from the plastic scintillatorelement, in particular in the downstream position. This layer can becomposed, completely or partially, of a material known to a personskilled in the art, for example chosen from greases, adhesives, gels,cements, elastomeric compounds, silicone compounds or their mixtures.

The coupling between the part and the electronic acquisition module canbe carried out directly or indirectly via the hybrid plasticscintillator element.

For example, this coupling is generally direct for the single hybridplastic scintillator element.

The coupling with the hybrid plastic scintillator element is, on theother hand, indirect in the case of the phoswich scintillator: thedownstream fast plastic scintillator element will be interposed betweenthese two parts, and it is the only one to be in direct contact with theelectronic acquisition module.

As regards the electronic acquisition module, it can comprise aphotodetector 3, for example chosen from a photo-multiplier, aphotodiode, a charge-coupled device CCD camera or a CMOS sensor.

The electronic acquisition module can be placed downstream, withreference to the direction of propagation of the ionizing radiation orof the ionizing particle with regard to the device, of the part ashybrid plastic scintillator element, of the single hybrid plasticscintillator element, of the first hybrid plastic scintillator element 1or of the second fast plastic scintillator element 2.

It can be calibrated in energy by virtue of standard scintillatingsubstances.

The invention also relates to an item of equipment for plasticscintillation detection comprising a device as defined in the presentdescription according to one or more of its alternative forms,constituted by a portable instrument for the detection of ionizingradiation, a walk-through scanner or a CCD (“Charge-Coupled Device”)detector.

The invention also relates to a process for the manufacture of a devicefor plastic scintillation detection as defined in the presentdescription according to one or more of its alternative forms, in whichthe part as hybrid plastic scintillator element is coupled (directly orindirectly) to the electronic acquisition module, so that the module iscapable of collecting the radioluminescent radiation emitted by the partwhen the latter is brought into contact with an ionizing radiation or anionizing particle.

The manufacturing process can be such that the device comprises aplastic scintillator assembly, the process comprising the followingsuccessive steps:

a″) having available a first hybrid plastic scintillator element 1 aspart and having available a second fast plastic scintillator element 2,the fluorescence decay constant of which is less than that of the firsthybrid plastic scintillator element 1; each of these plasticscintillator elements further having a polished surface of the samedimension as that of the other plastic scintillator element;

b″) coupling, via their polished surface, the first hybrid plasticscintillator element 1 and the second fast plastic scintillator element2, in order to obtain the plastic scintillator assembly;

c″) coupling the plastic scintillator assembly, comprising the part, tothe electronic acquisition module, so that the module is capable ofcollecting the radioluminescent radiation emitted by the plasticscintillator assembly when the latter is brought into contact with anionizing radiation or an ionizing particle.

According to a first embodiment, the process for the manufacture of thedevice is a process of autogenous coupling by thermal bonding: step b″)of bonding by coupling can be carried out by heating the polishedsurface of the first hybrid plastic scintillator element 1 and of thesecond fast plastic scintillator element 2 in order to soften thesesurfaces, which are subsequently pressed against one another in order tocouple them.

According to a second embodiment, the process for the manufacture of thedevice comprising a plastic scintillator assembly is a molecularautogenous coupling process (namely autogenous in situ), the processcomprising the following successive steps:

a′″) a plastic scintillator element, constituted by a first hybridplastic scintillator element 1 as part of or by a second fast plasticscintillator element 2, the fluorescence decay constant of which is lessthan that of the first hybrid plastic scintillator element 1, ismanufactured in situ by polymerization on the other plastic scintillatorelement, which constitutes a polymerization support, in order to obtaina plastic scintillator assembly on conclusion of step a′″);

b′″) the plastic scintillator assembly comprising the part is coupled tothe electronic acquisition module, so that the module is capable ofcollecting the radioluminescent radiation emitted by the plasticscintillator assembly when the latter is brought into contact with anionizing radiation or an ionizing particle.

The coupling between the plastic scintillator elements 1 and 2 accordingto step b″), and/or the coupling according to which the electronicacquisition module is coupled with the plastic scintillator assemblyaccording to step c″) or step b′″) or with the single hybrid plasticscintillator element as defined in the present description according toone or more of its alternative forms, can be carried out by means of anoptical interface layer 6.

The optical interface layer 6 can be an optical cement (for example ofEJ-500 type), a “coupling” solvent (generally an alcohol, such as, forexample, isopropanol or 1-butanol) or, preferably, an optical grease(for example of RTV141A type).

This interface layer generally has a thickness from 1 μm to 10 μm.

The invention also relates to a plastic scintillation measurementmethod, the method comprising the following successive steps:

i) a device for plastic scintillation detection as defined in thepresent description, among others according to one or more of itsalternative forms, is brought into contact with an ionizing radiation oran ionizing particle in order for the part (by virtue of the hybridmaterial which it contains) comprised in the device to emitradioluminescent radiation; and

ii) the radioluminescent radiation is measured with the electronicacquisition module of the device.

Preferentially, the duration of the decay in the radio-luminescentradiation measured is comprised between 10 ns and 90 ns, morepreferentially still between 15 ns and 80 ns, more preferentially stillbetween 30 ns and 80 ns, particularly between 25 ns and 75 ns, moreparticularly between 28 ns and 70 ns.

The ionizing radiation or the ionizing particle can originate from aradioactive substance which emits gamma rays, X-rays, beta particles,alpha particles or neutrons. If appropriate, the radioactive substancecan emit several types of ionizing radiation or of ionizing particles.Thus, advantageously, the gamma rays and the beta particles can bedistinguished by virtue of the shape of the different pulses during themeasurement step b) with the scintillation measurement method of theinvention.

The radioluminescent radiation which results from this exposure can bemeasured according to step ii) with a photodetector, such as, forexample, a photodetector chosen from a photomultiplier, a photodiode, acharge-coupled device (CCD) camera, a CMOS (“Complementary Metal-OxideSemiconductor”) sensor or any other photon detector, of which thecapture is converted into an electrical signal.

According to a preferential embodiment of the invention, the measurementmethod can comprise a step iii) in which the presence and/or the amountof the radioactive substance is determined from the measurement of theradio-luminescent radiation according to step ii), as is ordinarilycarried out in plastic scintillation. By way of example, the qualitativeand/or quantitative measurement step iii) is described by making theanalogy with the plastic scintillation from the document “Techniques del'ingénieur, Mesures de radioactivité par scintillation liquide,Reference p2552, publication du Oct. 3, 2004” [Techniques of theEngineer, Measurements of radioactivity by liquid scintillation,Reference p2552, publication of Oct. 3, 2004] [reference 10].

The quantitative determination can among others measure the activity ofthe radioactive source. It can be carried out from a calibration curve.

This curve is, for example, such that the number of photons originatingfrom the radioluminescent radiation emitted for a known radioactivesubstance is correlated with the energy of the incident radiation forthis radioactive substance. It is then possible, from the solid angle,from the distance between the radioactive source and the plasticscintillator, and from the activity detected by the measurement methodusing the plastic scintillator of the invention, to quantify theactivity of the radioactive source.

The invention also relates to a polymerization composition formanufacturing a hybrid material (as defined in the present description,according to one or more of its alternative forms) for plasticscintillation detection comprising:

-   -   monomers, oligomers or their mixtures intended to form at least        one constituent polymer of a polymeric matrix as defined in the        present description according to one or more of the alternative        forms;    -   a liquid fluorescent mixture comprising, in a molar        concentration with respect to the total number of moles of        primary fluorophore in the liquid fluorescent mixture;

i) from 80 molar % (more specifically 80.0 molar %) to 99.6 molar %(indeed even from 90 molar % (more specifically 90.0 molar %) to 99.1molar %, indeed even from 96 molar % (more specifically 96.0 molar %) to99.1 molar %) of a main primary fluorophore consisting of naphthalene;and

ii) from 0.4 molar % to 20 molar % (more specifically 20.0 molar %) ofan additional primary fluorophore, the centroid of the light absorptionspectrum and of the fluorescence emission spectrum of which respectivelyhave a wavelength comprised between 250 nm and 340 nm and comprisedbetween 330 nm and 380 nm, the fluorescence decay constant of which iscomprised between 1 ns and 10 ns and the fluorescence quantum yield in anonpolar solvent of which is comprised between 0.2 and 1 (indeed evenbetween 0.5 and 1).

According to a specific embodiment of the polymerization compositionaccording to the invention, the liquid fluorescent mixture can comprisei) from 95.6 molar % to 99.1 molar % of the main primary fluorophoreconsisting of naphthalene and ii) from 0.9 molar % to 4.4 molar % of theadditional primary fluorophore.

The monomers, the oligomers and their mixtures can comprise at least onearomatic, (meth)acrylic or vinyl group.

The liquid fluorescent mixture can comprise a secondary fluorophore, asdefined in the present description, according to one or more of itsalternative forms.

Thus, according to some of these alternative forms, the secondaryfluorophore can have:

-   -   a light absorption spectrum and a fluorescence emission        spectrum, the centroid of which is respectively at a wavelength        comprised between 330 nm and 380 nm and comprised between 405 nm        and 460 nm, and the fluorescence quantum yield in a nonpolar        solvent of which is comprised between 0.5 and 1, or;    -   a light absorption spectrum and a fluorescence emission        spectrum, the centroid of which is respectively at a wavelength        comprised between 330 nm and 380 nm and comprised between 460 nm        and 550 nm, and the fluorescence quantum yield in a nonpolar        solvent of which is comprised between 0.5 and 1, or;    -   a light absorption spectrum and a fluorescence emission        spectrum, the centroid of which is respectively at a wavelength        comprised between 330 nm and 380 nm and comprised between 550 nm        and 630 nm, and the fluorescence quantum yield in a nonpolar        solvent of which is comprised between 0.5 and 1.

The secondary fluorophore can be at a concentration by weight, withrespect to the weight of the polymerization composition, which iscomprised between 0.002% and 0.5% by weight.

The polymerization composition can comprise from 1% by weight to 25% byweight of the liquid fluorescent mixture.

It can also further comprise a polymerization solvent.

The polymerization composition can be employed in the processes for themanufacture of the hybrid material or of the part as were describedabove.

The invention also relates to a ready-for-use kit with mixedfluorophores for the manufacture of a polymerization composition (asdefined in the present description, according to one or more of itsalternative forms) comprising, separately for the purpose of theassembling thereof, the following components of the kit:

i) monomers, oligomers or their mixtures intended to form at least oneconstituent polymer of a polymeric matrix and;

ii) a fluorescent mixture for a polymerization kit comprising, as amolar concentration with respect to the total number of moles of primaryfluorophore in the fluorescent mixture for a polymerization kit:

i) from 80 molar % (more specifically 80.0 molar %) to 99.6 molar % of amain primary fluorophore consisting of naphthalene; and

ii) from 0.4 molar % to 20 molar % (more specifically 20.0 molar %) ofan additional primary fluorophore, the centroid of the light absorptionspectrum and of the fluorescence emission spectrum of which respectivelyhave a wavelength comprised between 250 nm and 340 nm and comprisedbetween 330 nm and 380 nm, the fluorescence decay constant of which iscomprised between 1 ns and 10 ns and the fluorescence quantum yield in anonpolar solvent of which is comprised between 0.2 and 1 (indeed evenbetween 0.5 and 1).

As regards the composition and the proportion of its components, thefluorescent mixture for a polymerization kit is identical to the liquidfluorescent mixture described above. However, when it does not comprisea solvent, it differs from the liquid fluorescent mixture solely in thefact that it is then in the solid form and not the liquid form.

The ready-for-use kit with mixed fluorophores can comprise:

-   -   a first compartment I) containing the monomers, the oligomers or        their mixtures;    -   a second compartment II) containing the fluorescent mixture for        a polymerization kit.

The fluorescent mixture for a polymerization kit can contain from 90molar % (more specifically 90.0 molar %) to 99.1 molar % (indeed evenfrom 96 molar % (more specifically 96.0 molar %) to 99.1 molar %) of themain primary fluorophore. It can represent from 1% by weight to 25% byweight of the components of the kit.

According to a specific embodiment of the invention, the fluorescentmixture for a polymerization kit can comprise i) from 95.6 molar % to99.1 molar % of the main primary fluorophore consisting of naphthaleneand ii) from 0.9 molar % to 4.4 molar % of the additional primaryfluorophore.

The ready-for-use kit with mixed fluorophores can be such that asecondary fluorophore as defined in the present description according toone or more of its alternative forms, a polymerization solvent or theirmixture is mixed with the i) monomers, oligomers or their mixturesand/or ii) the fluorescent mixture for a polymerization kit.

Typically, the secondary fluorophore can be mixed at the same molarconcentration with the i) monomers, oligomers or their mixtures and withii) the fluorescent mixture for a polymerization kit, in order toprevent, if necessary, any phenomenon of dilution.

Typically, the polymerization solvent can be mixed with the monomers andoligomers.

The invention also relates to a ready-for-use kit with separatefluorophores for the manufacture of a polymerization composition (asdefined in the present description, according to one or more of itsalternative forms) comprising, separately for the purpose of theassembling thereof, the following components of the kit:

i′) a first polymerization mixture comprising monomers, oligomers ortheir mixtures intended to form at least one constituent polymer of apolymeric matrix as defined in the present description according to oneor more of its alternative forms; and, in a molar concentration withrespect to the total number of moles of primary fluorophore in the kit,from 80 molar % (more specifically 80.0 molar %) to 99.6 molar % (indeedeven from 90 molar % (more specifically 90.0 molar %) to 99.1 molar %,indeed even from 96 molar % (more specifically 96.0 molar %) to 99.1molar %) of a main primary fluorophore consisting of naphthalene;

ii′) a second polymerization mixture comprising monomers, oligomers ortheir mixtures intended to form at least one constituent polymer of apolymeric matrix as defined in the present description according to oneor more of its alternative forms; and, at a molar concentration withrespect to the total number of moles of primary fluorophore in the kit,from 0.4 molar % to 20 molar % (more specifically 20.0 molar %) of anadditional primary fluorophore, the centroid of the light absorptionspectrum and of the fluorescence emission spectrum of which respectivelyhave a wavelength comprised between 250 nm and 340 nm and comprisedbetween 330 nm and 380 nm, the fluorescence decay constant of which iscomprised between 1 ns and 10 ns and the fluorescence quantum yield in anonpolar solvent of which is comprised between 0.2 and 1 (indeed evenbetween 0.5 and 1).

Thus, according to specific embodiments of the invention:

-   -   the first polymerization mixture can comprise from 90 molar %        (more specifically 90.0 molar %) to 99.1 molar % of the main        primary fluorophore consisting of naphthalene and the second        polymerization mixture can comprise from 0.9 molar % to 10 molar        % (more specifically 10.0 molar %) of the additional primary        fluorophore;    -   the first polymerization mixture can comprise from 96 molar %        (more specifically 96.0 molar %) to 99.1 molar % of the main        primary fluorophore consisting of naphthalene and the second        polymerization mixture can comprise from 4 molar % (more        specifically 4.0 molar %) to 0.9 molar % of the additional        primary fluorophore.

According to another specific embodiment of the invention, the firstpolymerization mixture can comprise from 95.6 molar % to 99.1 molar % ofthe main primary fluorophore consisting of naphthalene and the secondpolymerization mixture can comprise from 0.9 molar % to 4.4 molar % ofthe additional primary fluorophore.

The ready-for-use kit with separate fluorophores can comprise:

-   -   a first compartment I′) containing the first polymerization        mixture;    -   a second compartment II′) containing the second polymerization        mixture.

The first polymerization mixture and/or the second polymerizationmixture can comprise a secondary fluorophore as defined in the presentdescription according to one or more of its alternative forms, apolymerization solvent or their mixture.

As regards the ready-for-use kit with mixed fluorophores of theready-for-use kit with separate fluorophores:

-   -   the monomers, oligomers or their mixtures can represent from 75%        by weight to 99% by weight of the components of the kit, and/or;    -   the main primary fluorophore can represent from 1% by weight to        25% by weight of the components of the kit, and/or;    -   it can further comprise at least one ancillary compartment each        containing III) a crosslinking agent or a polymerization        initiator.

The ready-for-use kit with mixed fluorophores or the ready-for-use kitwith separate fluorophores can be such that the additional primaryfluorophore can represent from 0.006% by weight to 5% by weight of thecomponents of the kit. This is because the concentration of the mainprimary fluorophore in the first polymerization mixture can be comprisedbetween 1% by weight and 25% by weight, with respect to the monomers oroligomers, this being the case in order to prevent an a posterioriphenomenon of exudation in the polymeric matrix, as indicated above. Theconcentration of the additional primary fluorophore in the secondpolymerization mixture can also be 25% by weight, with respect to themonomers or oligomers, i.e. a maximum concentration of 25%×20%=5% in thecase of a mixture with the maximum of main primary fluorophore([c]max=25%) with the maximum proportion of additional primaryfluorophore ([c]max=20%). The same calculation for the minimumconcentration is 1%×0.6%=0.006%.

The invention also relates to a ready-for-use kit with polymers for themanufacture of an extrusion mixture (as defined in the presentdescription, according to one or more of its alternative forms)comprising, separately for the purpose of the assembling thereof, thefollowing components of the kit:

i″) polymerized ingredients (optionally in the form of granules)intended to form a polymeric matrix as defined in the presentdescription according to one or more of its alternative forms;

ii”) a fluorescent mixture for an extrusion kit comprising, at a molarconcentration with respect to the total number of moles of primaryfluorophore in the fluorescent mixture for an extrusion kit:

i) from 80 molar % (more specifically 80.0 molar %) to 99.6 molar %(indeed even from 90 molar % (more specifically 90.0 molar %) to 99.1molar %, indeed even from 96 molar % (more specifically 96.0 molar %) to99.1 molar %) of a main primary fluorophore consisting of naphthalene;and

ii) from 0.4 molar % to 20 molar % (more specifically 20.0 molar %) ofan additional primary fluorophore, the centroid of the light absorptionspectrum and of the fluorescence emission spectrum of which respectivelyhave a wavelength comprised between 250 nm and 340 nm and comprisedbetween 330 nm and 380 nm, the fluorescence decay constant of which iscomprised between 1 ns and 10 ns, and the fluorescence quantum yield ina nonpolar solvent of which is comprised between 0.2 and 1 (indeed evenbetween 0.5 and 1).

Thus, according to specific embodiments of the invention:

-   -   the fluorescent mixture for an extrusion kit can comprise from        90 molar % (more specifically 90.0 molar %) to 99.1 molar % of        the main primary fluorophore consisting of naphthalene and from        0.9 molar % to 10 molar % (more specifically 10.0 molar %) of        the additional primary fluorophore;    -   the fluorescent mixture for an extrusion kit can comprise from        96 molar % (more specifically 96.0 molar %) to 99.1 molar % of        the main primary fluorophore consisting of naphthalene and from        4 molar % (more specifically 4.0 molar %) to 0.9 molar % of the        additional primary fluorophore.

According to another specific embodiment of the invention, thefluorescent mixture for an extrusion kit can comprise from 95.6 molar %to 99.1 molar % of the main primary fluorophore consisting ofnaphthalene and from 0.9 molar % to 4.4 molar % of the additionalprimary fluorophore.

The polymerized ingredients have the same chemical composition as thepolymeric matrix. They differ from it essentially in the fact that theyare not in the bulk form, like the polymeric matrix, but in thedispersed form, for example in the form of granules.

The ready-for-use kit with polymers can comprise:

-   -   a first compartment I″) containing the polymerized ingredients;    -   a second compartment II″) containing the liquid fluorescent        mixture for an extrusion kit.

The ready-for-use kit with polymers can be such that a secondaryfluorophore as defined in the present description according to one ormore of its alternative forms, a polymerization solvent or their mixtureis mixed with i) the polymerized ingredients and/or ii) the fluorescentmixture for an extrusion kit.

The ready-for-use kit with polymers can also further comprise:

-   -   a secondary compartment containing the secondary fluorophore        and/or a polymerization solvent.

Each kit can comprise instructions giving the chart of the mixture to beproduced between the main primary fluorophore and the additional primaryfluorophore in order to obtain the desired fluorescence decay constant.

The components of each kit can be assembled, for the purpose of thesubsequent manufacture of the polymerization composition of theinvention, for the purpose among others of a use which is simultaneous,separate or spread out over time.

Other subject matters, characteristics and advantages of the inventionwill now be specified in the description which follows of specificembodiments of the invention, given by way of illustration and withoutlimitation, with reference to the appended FIGS. 1 to 8.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 represents a table in which the fluorescence decay constant ismeasured for hybrid materials which differ in the proportion between themain primary fluorophore and the additional primary fluorophore and inthe optional addition of a secondary fluorophore, and also, by way ofcomparison, for a material not containing an additional primaryfluorophore.

FIG. 2A represents the change in the fluorescence decay constant medianmonoexponential tau as a function of the molar proportion of the mainprimary fluorophore to the additional primary fluorophore according tothe data of FIG. 1. It can represent a chart appearing in theinstructions delivered with the ready-for-use kit.

By way of comparison, FIG. 2B represents the change in the fluorescencedecay constant median monoexponential tau as a function of the molarproportion of a main primary fluorophore different from that of theinvention to an additional primary fluorophore.

FIG. 3 represents the pulse profile for different plastic scintillators,namely the change in their responses in number of counts/seconds as afunction of the time, expressed in nanoseconds. A pulse recordingprofile is superimposed on these profiles.

FIG. 4 represents the energy spectra of a plastic scintillator of theinvention and of a commercial slow plastic scintillator.

FIGS. 5 and 6 represent a cross-sectional view of a device of “phoswich”type for plastic scintillation detection according to the invention,respectively without and with a bonding layer.

FIG. 7 represents an alternative form of the device of FIG. 6.

FIG. 8 represents the diagrammatic view of a scintillating optical fiberprovided with a sheath.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Unless otherwise indicated, the examples are carried out at atmosphericpressure and ambient temperature.

1. Manufacture of a Hybrid Material for Plastic ScintillationMeasurement According to the Invention.

1.1. Example 1 of Manufacture of a Plastic Scintillator with a SecondaryFluorophore.

A liquid mixture comprising fluorescent molecules (5% by weight (3.624g) of naphthalene as main primary fluoro-phore+0.2% by weight (183 mg)of 2,5-diphenyloxazole (PPO) as additional primary fluorophore and 0.02%by weight (15.2 mg) of 9,10-diphenylanthracene (DPA) as secondaryfluorophore), to which styrene (80 ml, i.e. 94.78% by weight) issubsequently added, is introduced into a single-necked round-bottomedflask dried beforehand under an inert argon atmosphere.

After five degassings under cold conditions under vacuum(“freeze-pump-thaw” method), the polymerization medium obtained,returned to ambient temperature, is poured into a mold capable of givingthe final shape to the plastic scintillator.

After heating the sealed mold under an inert argon atmosphere at 140° C.for five days, the plastic scintillator is removed from the mold,precision ground and then polished.

1.2. Example 2 of Manufacture of a Plastic Scintillator with a SecondaryFluorophore.

A liquid mixture comprising fluorescent molecules (5% by weight ofnaphthalene (3.624 g)+0.2% by weight of 2,5-diphenyloxazole (PPO, 183mg) as primary fluorophores and 0.02% by weight of1,4-bis(4-methyl-5-phenyl-2-oxazolyl)benzene (dimethylPOPOP, 15.2 mg) assecondary fluorophore), to which styrene (80 ml, 94.78% by weight) issubsequently added, is introduced into a single-necked round-bottomedflask dried beforehand under an inert argon atmosphere.

After five degassings under cold conditions under vacuum, thepolymerization medium obtained, returned to ambient temperature, ispoured into a mold.

After heating the sealed mold under an inert argon atmosphere at 140° C.for five days, the plastic scintillator is removed from the mold,precision ground and then polished.

1.3. Example 3 of Manufacture of a Plastic Scintillator with aCrosslinked Polymeric Matrix and a Secondary Fluorophore.

A liquid mixture comprising fluorescent molecules (5% by weight ofnaphthalene (3.624 g)+0.2% by weight of 2,5-diphenyloxazole (PPO, 183mg) as primary fluorophores and 0.02% by weight of9,10-diphenylanthracene (DPA, 15.2 mg) as secondary fluorophore), towhich 80% by weight of styrene (64 ml) and then 14.78% by weight of1,4-butanediyl dimethacrylate (10.3 ml) as crosslinking agent aresubsequently added, is introduced into a single-necked round-bottomedflask dried beforehand under an inert argon atmosphere.

After five degassings under cold conditions under vacuum, thepolymerization medium obtained, returned to ambient temperature, ispoured into a mold.

After heating the sealed mold under an inert argon atmosphere at 65° C.for ten days, the plastic scintillator is removed from the mold,precision ground and then polished.

2. Manufacture of a Range of Plastic Scintillators with a VariableProportion Between the Primary Fluorophores.

Plastic scintillators are manufactured according to the characteristicsspecified in the table of FIG. 1 according to a manufacturing processsimilar to that disclosed in the preceding examples.

They differ in the chemical composition of the polymeric matrix(St=polystyrene; St/1,4=mixture of styrene and of 1,4-butanediyldimethacrylate which are polymerized in a proportion by weight betweenthe two monomers respectively of 5 to 1) and in the molar ratio of themain primary fluorophore (naphthalene) to the additional primaryfluorophore (2,5-diphenyloxazole=PPO). The concentration by weight ofeach primary fluorophore is shown as percentage with respect to thetotal weight of the plastic scintillator, the remainder thus beingconstituted by the percentage by weight of the polymeric matrix, of theother primary fluorophore, and also by a constant concentration of 0.02%by weight of 9,10-diphenylanthracene (9,10-DPA) added as secondaryfluorophore, not shown in the table of FIG. 1.

The decay constant tau of the fluorescence is measured bytime-correlated single photon counting as described above. It is in thisinstance generally obtained by adjustment of biexponential type of thevalues obtained, weighting factors for each exponential component beingshown as percentage in brackets. In order to facilitate the comparisonbetween the different plastic scintillators, the biexponential tau isconverted into median monoexponential tau in accordance with theequation below, for which the quality of the adjustment of themeasurement with respect to the light pulse is evaluated by the chisquared, which should ideally be as close as possible to 1.Alternatively, commercial items of time-correlated single photoncounting equipment automatically calculate the median monoexponentialtau, indeed even the biexponential tau, from the data recorded.

The median decay constant monoexponential tau of the fluorescence can becalculated from the following formula:τ_(median)=τ_(fast)×%_(fast)+τ_(slow)×%_(slow)

The percentages “% fast” and “% slow” represent the respective weightsof the fast and slow decay. They are adjusted in order to give the bestpossible description of the median decay. Their sum is equal to 100%.

Thus, FIG. 2A represents the change in the fluorescence decay constantmedian monoexponential tau (median monoexponential tau) as a function ofthe naphthalene/PPO molar ratio. It clearly shows the continuous changein the fluorescence decay constant as a function of the molar ratio ofthe main primary fluorophore to the additional primary fluorophore. Thischange has the form of a decreasing exponential which is the signatureof a synergy between the main primary fluorophore and the additionalprimary fluorophore. In the absence of such a synergy, the change in thetime constant as a function of the molar ratio would be in the form of alinear line which would directly connect the value at 100% and at 0%,reflecting the simple gradual replacement of one primary fluorophore byanother.

By way of comparison, the main primary fluorophore according to FIG. 2Aof the naphthalene/PPO combination according to the invention wasreplaced by pyrene, a compound which belongs to the family of the fusedaromatic compounds, just like naphthalene, as is shown by the molecularstructures below:

The change in the fluorescence decay constant median monoexponential tau(median monoexponential tau) is studied as a function of the pyrene/PPOmolar ratio in a similar way to the study of FIG. 2A. The result isillustrated by FIG. 2B, which shows that this change absolutely does nothave the form of a decreasing exponential: there is thus no synergisticeffect between the pyrene and the PPO, unlike the combination of themain primary fluorophore and of the additional primary fluorophoreaccording to the invention.

Another advantage of the use of a hybrid material for the plasticscintillation measurement is demonstrated by FIG. 3, which illustratesthe type of response pulse obtained for a plastic scintillatorreferenced by an index in the figure:

-   -   fast (index a): “Eljen EJ-200” reference scintillator sold by        the Eljen Technology firm;    -   slow (index b): “Eljen EJ-240” reference scintillator sold by        the Eljen Technology firm;    -   hybrid (index c): comprising the hybrid material according to        the invention.

The recording profile used (500 ns with a noise of 10 counts/second) issuperimposed on the pulses of these three plastic scintillators.

FIG. 3 demonstrates the advantages of a phoswich plastic scintillatorcomprising a fast compartment and a hybrid compartment according to theinvention, in comparison with a phoswich plastic scintillator comprisinga fast compartment and a slow compartment: for an electronic noise forexample estimated at 10 counts per second, the hybrid pulse of thehybrid compartment has a better signal-to-noise ratio than the slowpulse of the slow compartment, by virtue of the greater amplitude of thehybrid pulse.

The acquisition is carried out by the opening of a time window forrecording these pulses. As indicated above, the duration of thisrecording is generally chosen in order to be from 6 to 10 times greaterthan the highest fluorescence decay constant, this decay constantcorresponding, for each pulse, to the width on the abscissa of thepulse, expressed in nanoseconds. In the case of high count rates, suchas, for example, when a radioactive source of high activity is broughtinto the presence of the phoswich device, the use of a slow compartmentthus involves using a much longer recording window: several pulses canthen coexist in the same time window (pile-up phenomenon), which is thenreflected by acquisition errors in the absence of discrimination ofthese pulses.

These properties of a hybrid compartment are thus particularlyadvantageous for the discrimination of the beta particle in anenvironment of gamma rays with a “phoswich” device comprising a hybridcompartment (in particular when it is the thinnest compartment) and afast compartment, each of these two compartments respectively detectingthe beta particle and the gamma radiation.

3. Example of Qualitative or Quantitative Measurement of a RadioactiveSubstance in Plastic Scintillation According to the Measurement Methodof the Invention.

3.1. Measurement Protocol.

A plastic scintillator comprising the hybrid material of the inventionin which a secondary fluorophore is incorporated is connected by meansof optical grease to a photomultiplier tube which performs the functionof photo-detector of an electronic acquisition module.

Subsequent to its exposure to the radioactive substance, the plasticscintillator emits scintillation photons which are converted into anelectrical signal by the photomultiplier tube supplied with highvoltage.

The electrical signal is subsequently acquired and then analyzed with anoscilloscope, spectrometry software or an electronic acquisition board.The data thus collected is subsequently processed by computer.

This analysis results in an energy spectrum histogram representing, onthe abscissa, the channels (derived from an output energy) and, on theordinate, the number of counts/second. After calibration with agamma-emitting source of known energy, the energy of the radioactivesubstance to be measured is determined.

3.2. Quantitative Measurement with the Scintillator.

On the basis of this measurement protocol, a quantitative measurement iscarried out with a chlorine-36 beta radioactive source of 4n activityequal to 6 kBq. This source is placed on the upper part of the plasticscintillator.

A cylindrical plastic scintillator of circular section, with a diameterof 49 mm and height of 35 mm (reference F30B of the table of FIG. 1) iscoupled with Rhodorsil RTV141A optical grease to the photocathode of aphotomultiplier (Hamamatsu H1949-51 model) supplied with a high voltage(Ortec 556 model). The signal leaving the photomultiplier is recoveredand then digitized by an electronic board specific to the inventor. Thisboard can be replaced by another equivalent electronic board (forexample CAEN DT5730B model) or an oscilloscope (for example LecroyWaverunner 640Zi model).

In a first step, an energy calibration of the system(scintillator+photomultiplier) is carried out by means of 2 radioactivesources: one emitting gamma rays in the [0-200 keV] range and the otherin the [500-1.3 MeV] range. This energy calibration is carried out bylocating the channel corresponding to 80% of the amplitude of theCompton edge.

For example, if the ordinate of the Compton edge corresponds to 100counts per second, the abscissa on the falling slope of the Compton edgeat 80 counts per second associates the energy of the Compton edge (inkeV) with the channel.

In a second step, this calibration having been carried out, thechlorine-36 beta source is joined to the upper face of the plasticscintillator. The analysis of the energy spectrum gives a read activityof 2.1 kBq (and thus an intrinsic efficiency according to which 70% ofthe incident radiation is measured) and a photoelectric peak centered atapproximately 250 keV.

The energy spectrum of the hybrid plastic scintillator obtained isrepresented in FIG. 4 (index (c′)). By way of comparison, it issuperimposed on that of a slow plastic scintillator (Eljen EJ-240 slow,sold by the Eljen Technology firm—index (b′) in FIG. 4), the measuredintrinsic efficiency of which is 54%.

4. Geometries of a Device for Plastic Scintillation Detection Accordingto the Invention.

Such a device is described with reference to FIGS. 5 and 6, whichrepresent, along a longitudinal axis with reference to the radiation R,sectional drawings of a plastic scintillator of parallelepipedal shapeof “phoswich” type. Thus, unless otherwise indicated, each part of thedevice represented here is of parallelepipedal shape. The same numericalreferences denote the same elements in these two figures.

4.1. Device with a Bonding Layer.

According to a first embodiment illustrated by FIG. 5, the plasticscintillation detection device D of the invention comprises a partaccording to the invention which is a first hybrid plastic scintillatorelement 1 constituted, completely or partially, of the hybrid materialof the invention and a second fast plastic scintillator element 2. Theseelements are respectively located upstream and downstream with respectto the direction R of propagation of the incident radiation (or of theincident particle) on the phoswich scintillator. Conventionally, theyare thus denoted in the continuation of the description by “upstreamhybrid scintillator 1” and “downstream fast scintillator 2”. In theconfiguration illustrated by FIG. 5, the upstream hybrid scintillator 1is referred to as “thin”, as it has a lower longitudinal thickness thanthe downstream fast scintillator 2, referred to as “thick. The devicefor plastic scintillation detection of the invention exhibiting allthese characteristics shows a discrimination between the gamma rays andthe beta particles which is improved.

The upstream hybrid scintillator 1 and the downstream fast scintillator2 are optionally contained in a shell 8 which can constitute the housingor the frame of the device. They are attached to one another with anoptical interface layer forming a bonding layer 5.

The bonding layer 5 is generally a layer distinct from the upstreamhybrid scintillator 1 and from the downstream fast scintillator 2, forexample an attaching layer. However, it can be a layer composed of anintermediate material resulting from the melting of the upstream hybridscintillator material 1 and of the downstream fast scintillator 2, asfor plastic scintillation detectors comprising two scintillators bondedto one another by thermomechanical pressing.

The bonding layer 5 can be an optical layer which is transparent toluminescent radiation. It can be composed of a bonding substance chosenfrom greases, adhesives, gels, optical cements, elastomeric compounds orsilicone compounds ordinarily employed in the optical field. Such asubstance allows the light radiation leaving the upstream scintillatorto pass.

A photodetector 3 (such as, for example, a photo-multiplier) is attachedto the downstream fast scintillator with an optical interface layer 6.It is capable of collecting the radioluminescent radiation resultingfrom the contact of an ionizing particle or of ionizing radiation withthe scintillators 1 and 2.

The face of the upstream hybrid scintillator 1 which first receives theincident radiation according to the direction of propagation R to bedetected is covered with a metal layer 4 which is in this instance thin.This metal layer constitutes an inlet window with which the incidentradiation (or the incident particle) comes into contact, whilepreventing the ambient light from also coming into contact with theupstream scintillator by isolating it from the light. The side faces ofthe upstream and downstream scintillators are covered with a lightreflector or diffuser 7 composed of a reflecting substance comprising,for example, aluminum (aluminized Mylar, aluminum paper, and the like)or composed of a scattering substance comprising, for example, Teflon, apaint based on titanium oxide TiO₂, a paint based on magnesium oxide MgOor Millipore filter paper.

4.2. Device without a Bonding Layer.

According to a second embodiment illustrated by FIG. 6, the plasticscintillation detection device D of the invention has a structure asdescribed in the document WO 2013076279 [reference 11]. It thus does notcomprise a bonding layer, such as the optical interface layer 5described in FIG. 5. The device for plastic scintillation detectionwithout a bonding layer of the invention nevertheless differs from thatdescribed in the reference [8] in that it comprises a first hybridplastic scintillator element constituted, completely or partially, ofthe hybrid material of the invention.

The plastic scintillation detection device D of the invention withoutthe bonding layer illustrated by FIG. 6, comprises a first hybridplastic scintillator element 1 constituted, completely or partially, ofthe hybrid material of the invention and a second fast plasticscintillator element 2. These elements are respectively located upstreamand downstream, with respect to the direction R of propagation ofincident radiation (or of the incident particle) on the phoswichscintillator. In the configuration illustrated by FIG. 5, the upstreamhybrid scintillator 1 is said to be “thin” as it has a lowerlongitudinal thickness than the downstream fast scintillator 2, said tobe “thick”. The device for plastic scintillation detection of theinvention exhibiting all these characteristics shows a discriminationbetween the gamma rays and the beta particles which is improved.

The upstream hybrid scintillator 1 and the downstream fast scintillator2 are in direct contact and are attached to one another by an autogenouscoupling process. In this coupling process, a first crosslinked plasticscintillator is prepared and then polymerized. After this first solidformulation, the monomer solution containing the fluorescence mixture inorder to manufacture the second scintillator is poured onto the firstscintillator, and the assembly is subsequently heated.

The scintillators 1 and 2 are optionally contained in a shell 8 whichcan constitute the housing or the frame of the device.

A photodetector 3 (such as, for example, a photo-multiplier) is attachedto the downstream fast scintillator with an optical interface layer 6.It is capable of collecting the radioluminescent radiation resultingfrom the contact of an ionizing particle or of ionizing radiation withthe scintillators 1 and 2.

The face of the upstream hybrid scintillator 1 which first receives theincident radiation (or the incident particle), according to thedirection of propagation R, to be detected is covered with alight-opaque layer 9. This opaque layer 9 constitutes an inlet windowwith which the incident radiation comes into contact, while limiting thecontact of the ambient light with the upstream scintillator.

The side faces of the upstream and downstream scintillators are coveredwith a light reflector or diffuser 7. The light-opaque layer 9 ispermeable to the passage of beta radiation and gamma radiation. It iscomposed of an opaque substance, such as, for example, Mylar.

As indicated above, the upstream hybrid scintillator 1 can have a lowerthickness than the downstream fast scintillator 2. Such a configurationis represented in FIG. 7.

4.3. Scintillating Optical Fiber.

FIG. 8 represents a scintillating optical fiber 10 of cylindricalsection. It comprises a polymer fiber 11 composed, completely orpartially, of the hybrid material of the invention. The polymer fiber 11constituting the internal core of the fiber is covered with a sheath 12covering the polymer fiber and composed, completely or partially, of asheathing material.

The present invention is not limited to the embodiments described andrepresented, and a person skilled in the art will know how to combinethem and to contribute thereto with his general knowledge of numerousalternative forms and modifications.

The invention is applicable to the fields where scintillators are used,in particular:

in the industrial field, for example for the measurement of physicalparameters of parts during manufacture, for the nondestructiveinspection of materials, for the monitoring of radioactivity at theentrance and exit points of sites and for the monitoring of radioactivewaste,

-   -   in the geophysical field, for example for the evaluation of the        natural radioactivity of soils,    -   in the field of fundamental physics and in particular nuclear        physics,    -   in the field of the safety of goods and people, for example for        the safety of critical infrastructures, the monitoring of moving        goods (luggage, containers, vehicles, and the like), and also        for the protection from radiation of workers in the industrial,        nuclear and medical sectors,    -   in the field of medical imaging.

REFERENCES CITED

-   [1] Moser, S. W.; Harder, W. F.; Hurlbut, C. R.; Kusner, M. R.,    “Principles and practice of plastic scintillator design”, Radiat.    Phys. Chem., 1993, vol. 41, No. 1/2, 31-36.-   [2] Bertrand, G. H. V.; Hamel, M.; Sguerra, F., “Current status on    plastic scintillators modifications”, Chem. Eur. J., 2014, 20,    15660-15685.-   [3] Wilkinson, D. H., “The Phoswich—A Multiple Phosphor”, Rev. Sci.    Instrum., 1952, 23, 414-417.-   [4] M. Wahl, “Time-Correlated Single Photon Counting”, Technical    instructions from PicoQuant, 2014.-   [5] D. V. O'Connor, D. Phillips, Time Correlated Single Photon    Counting, Academic Press, New York, 1984, pages 25 to 34.-   [6] Rohwer, L. S., Martin, J. E., “Measuring the absolute quantum    efficiency of luminescent materials”, J. Lumin., 2005, 115, pages    77-90.-   [7] Velapoli, R. A.; Mielenz, K. D., “A Fluorescence Standard    Reference Material: Quinine Sulfate Dihydrate”, Appl. Opt., 1981,    20, 1718.-   [8] WO 2013076281.-   [9] Techniques de l′ingenieur, Extrusion—extrusion monovis (partie    1), Reference AM3650, publication of 2002.-   [10] Techniques de l′ingenieur, Mesures de radioactivite par    scintillation liquide, Reference p2552, publication of Oct. 3, 2004.-   [11] WO 2013076279.

The invention claimed is:
 1. Hybrid material for plastic scintillation measurement comprising: a polymeric matrix; and a fluorescent mixture incorporated in the polymeric matrix and comprising, in a molar concentration with respect to the total number of moles of primary fluorophores in the incorporated fluorescent mixture: i) from 95.6 molar % to 99.1 molar % of a main primary fluorophore consisting of naphthalene; and ii) from 0.9 molar % to 4.4 molar % of an additional primary, fluorophore, the centroid of the light absorption spectrum and of the fluorescence emission spectrum of which have respectively a wavelength comprised between 250 nm and 340 nm and comprised between 330 nm and 380 nm, the fluorescence decay constant of which is comprised between 1 ns and 10 ns and the fluorescence quantum yield in a nonpolar solvent of which is comprised between 0.2 and
 1. 2. Hybrid material according to claim 1, wherein the incorporated fluorescent mixture comprises from 96 molar % to 99.1 molar % of the main primary fluorophore.
 3. Hybrid material according to claim 1, wherein the incorporated fluorescent mixture further comprises a secondary fluorophore.
 4. Hybrid material according to claim 3, wherein the secondary fluorophore is at a concentration by weight with respect to the weight of the hybrid material which is comprised between 0.002% and 0.5% by weight.
 5. Process for the manufacture of a hybrid material according to claim 1, by polymerization via a polymerization medium, the process comprising the following successive steps: a) having available a polymerization medium comprising: monomers, oligomers or their mixtures intended to form at least one constituent polymer of said polymeric matrix; a liquid fluorescent mixture comprising, in a molar concentration with respect to the total number of moles of primary fluorophores in the liquid fluorescent mixture: i) from 95.6 molar % to 99.1 molar % of a main primary fluorophore consisting of naphthalene; and ii) from 0.9 molar % to 4.4 molar % of an additional primary fluorophore, the centroid of the light absorption spectrum and of the fluorescence emission spectrum of which have respectively a wavelength comprised between 250 nm and 340 nm and comprised between 330 nm and 380 nm, the fluorescence decay constant of which is comprised between 1 ns and 10 ns, and the fluorescence quantum yield in a nonpolar solvent of which is comprised between 0.2 and 1; and b) polymerizing the polymerization medium in order to obtain the hybrid material.
 6. Part for plastic scintillation detection composed, completely or partially, of a hybrid material according to claim
 1. 7. Part for plastic scintillation detection according to claim 6, wherein the part has a: parallelepipedal shape and is a plastic scintillator compartment capable of being incorporated in a device for plastic scintillation detection; or cylindrical shape and is a scintillating optical fiber comprising a polymer fiber composed, completely or partially, of the hybrid material and provided or not provided with a sheath covering the polymer fiber and composed, completely or partially, of a sheathing material for an optical fiber, the refractive index of which is less than that of the hybrid material, the hybrid material comprising the polymeric matrix, wherein the polymeric matrix is constituted, completely or partially, of at least one polymer which is not crosslinked.
 8. Process for the manufacture by extrusion of a part for plastic scintillation detection and composed; completely or partially, of a hybrid material, the part being in accordance with claim 6, the process comprising the following successive steps: a′) having available an extrusion mixture comprising: polymerized ingredients intended to form said polymeric matrix; a fluorescent mixture for extrusion comprising, in a molar concentration with respect to the total number of moles of primary fluorophores in the fluorescent mixture for extrusion: i) from 95.6 molar % to 99.1 molar % of a main primary fluorophore consisting of naphthalene; and ii) from 0.9 molar % to 4.4 molar % of an additional primary fluorophore, the centroid of the light absorption spectrum and of the fluorescence emission spectrum of which respectively have a wavelength comprised between 250 nm and 340 nm and comprised between 330 nm and 380 nm, the fluorescence decay constant of which is comprised between 1 ns and 10 ns and the fluorescence quantum yield in a nonpolar solvent of which is comprised between 0.2 and 1; and b′) under an extrusion atmosphere at an extrusion temperature comprised between 70° C. and 200° C., extruding the extrusion mixture through a die in order to obtain the part composed, completely or partially, of a hybrid material.
 9. Process for the manufacture by polymerization of a part for plastic scintillation detection and composed, completely, or partially, of a hybrid material, the part being in accordance with claim 6, the process comprising at least one polymerization via a polymerization medium according to the following successive steps: a) in a first mold, having available a first polymerization medium comprising: monomers, oligomers or their mixtures intended to form at least one constituent polymer of said polymeric matrix; and a liquid fluorescent mixture comprising, in a molar concentration with respect to the total number of moles of primary fluorophores in the liquid fluorescent mixture: i) from 95.6 molar % to 99.1 molar % of a main primary fluorophore consisting of naphthalene; and ii) from 0.9 molar % to 4.4 molar % of an additional primary fluorophore, the centroid of the light absorption spectrum and of the fluorescence emission spectrum of which respectively have a wavelength comprised between 250 nm and 340 nm and comprised between 330 nm and 380 nm, the fluorescence decay constant of which is comprised between 1 ns and 10 ns and the fluorescence quantum yield in a nonpolar solvent of which is comprised between 0.2 and 1; and b) polymerizing the first polymerization medium in order to directly obtain the part or a preform of the part which is subsequently modified in order obtain the part.
 10. Device for plastic scintillation detection comprising a part according to claim 6 for plastic scintillation detection as a hybrid plastic scintillator element.
 11. Device for plastic scintillation detection according to claim 10, wherein the part has a parallelepipedal or cylindrical shape; the part of cylindrical shape being an scintillating optical fiber comprising a polymer fiber composed, completely or partially, of the hybrid material and provided or not provided with a sheath covering the polymer fiber and composed, completely or partially, of a sheathing material for an optical fiber, the refractive index of which is less than that of the hybrid material, the hybrid material comprising the polymeric matrix, wherein the polymeric matrix is constituted, completely or partially, of at least one polymer which is not crosslinked.
 12. Device for plastic scintillation detection according to claim 10, wherein the hybrid plastic scintillator element is a first hybrid plastic scintillator element, the device further comprising a second fast plastic scintillator element, the fluorescence decay constant of which is less than that of the first hybrid plastic scintillator element, these plastic scintillator elements forming a plastic scintillator assembly, the device being for example a device of phoswich type.
 13. Device for plastic scintillation detection according to claim 12, wherein the plastic scintillator elements have different thicknesses, so that the device comprises a thin plastic scintillator element and a thick fast scintillator element the thin first hybrid plastic scintillator element being upstream and the thick second fast plastic scintillator element being downstream, with reference to the direction R of propagation of the ionizing radiation or of the ionizing particle with regard to the device.
 14. Device for plastic scintillation detection according to claim 12, wherein the second fast plastic scintillator element comprises said polymeric matrix and a fast primary fluorophore chosen from 2,5-diphenyloxazole (PPO), para-terphenyl (pTP), meta-terphenyl (mTP), biphenyl, 2-phenyl-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD), 2-(4′-(t-butyl)phenyl)-5-(4″-biphenylyl)-1,3,4-oxadiazole (butyl-PBD), anthracene or their mixtures.
 15. Device for plastic scintillation detection according to claim 10, wherein the part comprises a single hybrid plastic scintillator element.
 16. Item of equipment for plastic scintillation detection comprising a device according to claim 10, constituted by a portable instrument for the detection of ionizing radiation, a walk-through scanner or a CCD detector.
 17. Process for the manufacture of a device for plastic scintillation detection according to claim 10, wherein the part as hybrid plastic scintillator element is coupled to the electronic acquisition module, so that the module is capable of collecting the radioluminescent radiation emitted by the part when the latter is brought into contact with an ionizing radiation or an ionizing particle.
 18. Plastic scintillation measurement method, the method comprising the following successive steps: i) a device according to claim 10 is brought into contact with an ionizing radiation or an ionizing particle in order for the part comprised in the device to emit radioluminescent radiation; and ii) the radioluminescent radiation is measured with the electronic acquisition module of the device.
 19. Scintillation measurement method according to claim 18, wherein the duration of the decay in the radioluminescent radiation measured is comprised between 25 ns and 75 ns.
 20. Scintillation measurement method according to claim 18, wherein the ionizing radiation or the ionizing particle originates from a radioactive substance which emits gamma rays and beta particles which are distinguished during the measurement step ii). 